Tensor algebra

 Computer Algebra  No Responses »
Jul 142021
 

The other day, someone asked a question: Can the itensor package in Maxima calculate the Laplace-Beltrami operator applied to a scalar field in the presence of torsion?

Well, it can. But I was very happy to get this question because it allowed me to uncover some long-standing, subtle bugs in the package that prevented some essential simplifications and in some cases, even produced nonsensical results.

With these fixes, Maxima now produces a beautiful result, as evidenced by this nice newly created demo, which I am about to add to the package:

(%i1) if get('itensor,'version) = false then load(itensor)
(%i2) "First, we set up the basic properties of the system"
(%i3) imetric(g)
(%i4) "Demo is faster in 3D but works for other values of dim, too" 
(%i5) dim:3
(%i6) "We declare symmetries of the metric and other symbols"
(%i7) decsym(g,2,0,[sym(all)],[])
(%i8) decsym(g,0,2,[],[sym(all)])
(%i9) components(g([a],[b]),kdelta([a],[b]))
(%i10) decsym(levi_civita,0,dim,[],[anti(all)])
(%i11) decsym(itr,2,1,[anti(all)],[])
(%i12) "It is useful to set icounter to avoid indexing conflicts"
(%i13) icounter:100
(%i14) "We choose the appropriate convention for exterior algebra"
(%i15) igeowedge_flag:true
(%i16) "Now let us calculate the Laplacian of a scalar field and simplify"
(%i17) canform(hodge(extdiff(hodge(extdiff(f([],[]))))))
(%i18) contract(expand(lc2kdt(%)))
(%i19) ev(%,kdelta)
(%i20) D1:ishow(canform(%))
                  %1 %2  %3 %4                 %1 %2            %1 %2
(%t20)   (- f    g      g      g     ) + f    g      + f       g
             ,%4  ,%3           %1 %2     ,%2  ,%1      ,%1 %2
(%i21) "We can re-express the result using Christoffel symbols, too"
(%i22) ishow(canform(conmetderiv(D1,g)))
               %1 %4  %2 %5      %3                   %1 %2      %3
(%t22) 2 f    g      g      ichr2      g      - f    g      ichr2
          ,%5                    %1 %2  %3 %4    ,%3             %1 %2
                                              %1 %3      %2               %1 %2
                                      - f    g      ichr2      + f       g
                                         ,%3             %1 %2    ,%1 %2
(%i23) "Nice. Now let us repeat the same calculation with torsion"
(%i24) itorsion_flag:true
(%i25) canform(hodge(extdiff(hodge(extdiff(f([],[]))))))
(%i26) "Additional simplifications are now needed"
(%i27) contract(expand(lc2kdt(%th(2))))
(%i28) ev(%,kdelta)
(%i29) canform(%)
(%i30) ev(%,ichr2)
(%i31) ev(%,ikt2)
(%i32) ev(%,ikt1)
(%i33) ev(%,g)
(%i34) ev(%,ichr1)
(%i35) contract(rename(expand(canform(%))))
(%i36) flipflag:not flipflag
(%i37) D2:ishow(canform(%th(2)))
                %1 %2  %3 %4                 %1 %2    %3            %1 %2
(%t37) (- f    g      g      g     ) + f    g      itr      + f    g
           ,%1         ,%2    %3 %4     ,%1           %2 %3    ,%1  ,%2
                                                                          %1 %2
                                                               + f       g
                                                                  ,%1 %2
(%i38) "Another clean result; can also be expressed using Christoffel symbols"
(%i39) ishow(canform(conmetderiv(D2,g)))
               %1 %2  %3 %4      %5                   %1 %2    %3
(%t39) 2 f    g      g      ichr2      g      + f    g      itr
          ,%1                    %2 %3  %4 %5    ,%1           %2 %3
                     %1 %2      %3            %2 %3      %1               %1 %2
             - f    g      ichr2      - f    g      ichr2      + f       g
                ,%1             %2 %3    ,%1             %2 %3    ,%1 %2
(%i40) "Finally, we see that the two results differ only by torsion"
(%i41) ishow(canform(D2-D1))
                                   %1 %2    %3
(%t41)                       f    g      itr
                              ,%1           %2 %3
(%i42) "Last but not least, d^2 is not nilpotent in the presence of torsion"
(%i43) extdiff(extdiff(f([],[])))
(%i44) ev(%,icc2,ikt2,ikt1)
(%i45) canform(%)
(%i46) ev(%,g)
(%i47) ishow(contract(%))
                                       %3
(%t47)                         f    itr
                                ,%3    %275 %277
(%i48) "Reminder: when dim = 2n, the Laplacian is -1 times these results."

The learning curve is steep and there are many pitfalls, but itensor remains an immensely powerful package.

 Posted by at 3:51 pm

Updated COVID maps

 Health  No Responses »
Jul 142021
 

I was looking for something else in my blog when I came across this post of mine from last May, putting my rusty R programming skills to use and producing some maps representing COVID-19 statistics.

Needless to say, the situation is quite different today, but in some ways at least, the more things change the more they remain the same.

The number of cases per million people is up, way up of course.

However, the trend remains the same: the worst numbers come from Europe and the Americas. I still cannot decide if this is a characteristic of COVID-19 or simply a result of more thorough testing and more transparent reporting in liberal democracies.

The death statistic is also similar:

The reddest areas are again the Americas and Europe, including Russia, but also Iran. The encouraging news is that the death rate per million didn’t rise quite as fast as the number of cases per million population. This may indicate that we have become more successful treating people (of course a more sinister possibility is that the most vulnerable, such as the elderly in homes, died first, pushing up last year’s death statistic.)

To see this more clearly, here is the mortality rate, that is, the percentage of deaths per cases:

Last year, North America and Europe, along with China, led the pack. This year, it’s quite different: both North America and Western Europe have fallen behind, which is to say, fewer people who catch COVID-19 actually die.

Another difference of course is that we can now protect ourselves and others around us by getting vaccinated. So please, do not hesitate, do not buy into insane conspiracy theories. Vaccines carry a tiny risk, but so does stepping outside to do your shopping, because you never know when a wayward car might jump the curb and kill you. But vaccines also protect you from a debilitating illness that often cripples even its survivors with lasting health effects. And no, vaccines are not an evil plot by Gates or Soros to get you microchipped; the technology just doesn’t work that way. Similarly, no, 5G cellular technology, which is mostly about using radio waves more efficiently, often with less power than current networks, has nothing to do with biology. Last but not least, whether the virus came from bats or a lab (there is little doubt in the literature that it is of natural origin, but that does not exclude the possibility that it was released from a lab by accident — such accidents are known to have happened even in high biosafety labs around the world) makes no difference: in the end, it can kill or maim you just the same, and the best way to protect yourself and your loved ones is through vaccination and responsible behavior (masks, distancing). In short (and with apologies for preaching): it’s not politics, people. It’s epidemiology.

 Posted by at 1:30 pm

Spoilers and selfies

 Art, History, Humor, Hungary  No Responses »
Jun 302021
 

Yesterday, I saw an image of a beautiful altarpiece, Dutch painter Rogier van der Weyden’s Santa Columba triptych from 1455.

It was described as the biggest spoiler in history. Look at the center panel depicting the classic Nativity scene. Now look more closely at the center column:

Oops.

And then, I saw another image, a 1958 photo from Pál Berkó, courtesy of the Hungarian Fortepan photo archive, depicting the crowd greeting Khrushchov on account of his visit to Budapest. Greeting him with… smartphones in hand, taking selfies?

Not exactly. Those are actually mirrors that many used to be able to see over the crowd. But the resemblance is…

I guess it’s true: The more we change, the more we remain the same.

 Posted by at 8:03 pm

49.6

 Canada, Weather and Climate  No Responses »
Jun 292021
 

Temperatures like this just do not exist in Canada.

When you hear that the temperature was within a hair’s breadth of 50 degrees centigrade (well over 120 F) you’d think I am talking about a spot in the Sahara Desert. Or maybe the Australian Outback. Or Death Valley.

But no, this temperature was measured earlier today in Lytton, British Columbia, Canada.

It is surreal. Scary. And deadly: apparently, dozen’s of mostly older people succumbed to this heat wave in BC.

 Posted by at 10:33 pm

A National Crime

 Canada, History, Local Ottawa  No Responses »
Jun 262021
 

Recently, it felt at times almost like a fad: Questioning the legacy of past celebrities, removing statues, renaming institutions.

Often, it seemed like these denounced heroes of the past are held to an impossible standard: Not living up to the changing values of the present.

I questioned the motivation: Was it true concern that we worship the wrong heroes, or just a cheap attempt at “virtue signaling”? I questioned the outcome: Exactly how does renaming a high school or removing a statue from a public park help an Indigenous community get safe drinking water, better jobs, better health care?

But more importantly, I questioned the wisdom of judging the past by the standards of the present. Standards that evolve and (thankfully!) improve, but which, for that very reason, would have been impossible for our past heroes to live up to, as those standards did not yet exist.

Faced with the discovery of the unmarked graves of many hundreds of Canadian children that is reopening the wounds of the despicable residential school system, I was wondering the same thing. Were these schools really the manifestations of evil? Or were they perhaps no different from other residential schools for the poor, for the children of immigrants, for other disadvantaged members of a society that, let’s face it, was quite bigoted by present-day standards?

But now I have my answer. What took place in those schools a century ago was not normal, not acceptable. It was criminal, even by the standards of early-1900s Canada. It’s just that nobody cared.

How do I know? From the accounts of someone who was in a unique position to critique the system: Peter Henderson Bryce, who at one point served as Canada’s Chief Medical Officer at the Department of Immigration.

For many years, Bryce studied the health of Canada’s Indigenous population, specifically the conditions at the residential schools. He was appalled by what he saw as an underfunded system of unsanitary, crowded facilities with shockingly high mortality rates. His report was suppressed and he was instead eventually pushed out of the Civil Service. Refusing to be silenced, he published his report himself.

The title says it all:

A National Crime

So there we have it. We are not misapplying our much improved, enlightened standards of 2021 to judge people and institutions that existed a century ago. What they did back then, how they treated the Indigenous population of Canada was A National Crime even by the standards of a contemporary member of the establishment, a dedicated civil servant who was already a teenager when the Dominion of Canada was established in 1867.

Dr. Peter Bryce, M. D., who passed away in 1932 at the age of 78, is buried not far from our home, right here in Ottawa, in the famed Beechwood Cemetery.

 Posted by at 7:56 pm

Second dose

 Health, Personal  No Responses »
Jun 262021
 

My beautiful wife and I both received our second jabs today.

Our first dose was AstraZeneca, but it is now recommended to choose an mRNA vaccine for the second dose. My remaining concern is whether this mixed shot is good enough to enter other countries, the United States in particular, where the AZ vaccine never received emergency FDA approval. We shall see… worst case, I guess, is that we will need a third dose.

 Posted by at 1:37 pm

A broken society

 Canada, Politics  No Responses »
Jun 082021
 

I am reacting with horror to the killing of a Muslim family in London, Ontario, by a deranged lunatic who mowed them down with his vehicle.

Yumna Afzaal (15), Madiha Salman (44), Talat Afzaal (74) and Salman Afzaal (46).

What drives a man to massacre an entire family, including children, as they are waiting to cross the street at an intersection?

And how do we fix this?

It is very easy to ascribe the attack to racism or “white grievance” (his race was not publicized but one press image surfaced that shows him to be of European descent) and chances are, it would not be the wrong conclusion. But if we stop there, we have solved nothing. The problems will persist, more people will die, and our society will become more polarized over time.

That is not to suggest that I know how to solve this problem. But I know what not to do. This is best illustrated by a quote that is often wrongly attributed to Nelson Mandela (it actually comes from a human rights activist named Mohamad Safa):

Our world is not divided by race, color, gender or religion. Our world is divided into wise people and fools. And fools divide themselves by race, color, gender, or religion.

I agree with the sentiment, but I ask a question that, in my opinion, is really the key to it all: How do we convince wise people (or people who think of themselves as wise) not to divide us into wise people and fools?

 Posted by at 6:04 pm

A serious thought about the Wuhan lab

 Health, Politics  No Responses »
May 302021
 

A few days ago, I posted an old Far Side cartoon about an accident at a virology lab. It was intended as humor, appropriate in light of the announcement that the US government seeks additional information concerning the possible role of the Wuhan virology lab in the pandemic. This investigation was triggered by the revelation that back in November 2019, researchers from that lab became sick with symptoms similar to those of COVID-19, compounded by secrecy by the Chinese government.

I think this investigation is warranted. I do not prejudge its outcome.

I do feel it is important to mention, however, that there is a difference between engineering a virus vs. releasing a virus. The fact that COVID-19 is not an engineered virus was well-established early on. Conclusions can of course change in the light of new information but I don’t think there is much room for change here. It has all the hallmarks of a virus that jumped from animals to humans (which such viruses, I am told, often do) and none of the hallmarks of a bioengineered virus. So I think in light of that it is quite unlikely that the virus was the result of, e.g., a botched bioweapons experiment or worse yet, an intentional pandemic.

Could it have been accidentally released? That’s another story altogether. The mandate of the Wuhan lab, I understand, is to research illnesses such as SARS or COVID-19. This lab produced many research papers over the years warning the world that a much more serious pandemic than the SARS epidemic is possible, even likely. Those papers were prophetic, but largely unheeded. It would be ironic if the same lab was found responsible in the end for causing the very pandemic that it tried to help prevent, and if the Chinese government played a role in suppressing information that, early on, could have saved many lives, they should be held responsible.

But for now, we don’t know if any of this is true. The Far Side cartoon was not intended to imply anything. It is just… funny, and uncannily prophetic. Just like the Wuhan lab’s research papers from years past.

 Posted by at 11:51 am

Algebra and wave optics

 Personal, Physics  No Responses »
May 182021
 

We have a new manuscript on arXiv. Its title might raise some eyebrows: Algebraic wave-optical description of a quadrupole gravitational lens.

Say what? Algebra? Wave optics? Yes. It means that in this particular case, namely a gravitational lens that is described as a gravitational monopole with a quadrupole correction, we were able to find a closed form description that does not rely on numerical integration, especially no numerical integration of a rapidly oscillating function.

Key to this solution is a quartic equation. Quartic equations were first solved algebraically back in the 16th century by Italian mathematicians. The formal solution is usually considered to be of little practical value, as it entails cumbersome algebra, and polynomial equations can be routinely and efficiently solved using numerical methods.

But in this case… The amazing thing is that the algebraic solution reveals so much about the physics itself!

Take this figure from our paper, for instance:

On the left is light projected by the gravitational lens, its so-called point-spread function (PSF) which tells us how light from a point source is distributed on an imaginary projection screen by the lens. On the right? Why, that’s the discriminant of the quartic equation

$$ x^4-2\eta\sin\mu \, x^3+\big(\eta^2-1\big)x^2+\eta\sin\mu \, x+{\textstyle\frac{1}{4}}\sin^2\mu=0, $$

in a plane characterized by polar coordinates \((\eta,\tfrac{1}{2}\mu)\), that is, \(\eta\) as a radial coordinate and \(\tfrac{1}{2}\mu \) as an azimuthal angle. When the discriminant is positive, the equation is expected to have four real (or four complex) roots; everywhere else, it’s a mix of real and imaginary roots. This direct connection between the algebra and the lensing phenomenon is unexpected and beautiful.

The full set of real roots of this equation can be shown in the form of an animation:

Of course one must read the paper in order for this animation to make sense, but I think it’s beautiful.

How good is this quartic solution? It is uncannily accurate. Here is a comparison of the PSF computed using the quartic solution and also using numerical integration, as well as some enlarged details from the so-called caustic boundary:

It’s only in the immediate vicinity of the caustic boundary that the quartic solution becomes less than accurate.

We can also use the quartic solution to simulate images seen through a telescope (i.e., the Einstein ring, or what survives of it, that would appear around a gravitational lens when we looked at the lens through a telescope with a point source of light situated behind the lens.) We can see again that it’s only in the vicinity of the caustic boundary that the quartic solution produces artifacts instead of accurately reproducing it when spots of light widen into arcs:

This paper was so much joy to write! Also, for the first time in my life, this paper gave us a legitimate, non-pretentious reason to cite something from the 16th century: Cardano’s 1545 treatise in which the quartic solution (as well as the cubic) are introduced, together with discussion on the meaning of taking the square root of negative numbers.

 Posted by at 5:35 pm

Esile Rüf

 Humor, Music  No Responses »
May 142021
 

No, it’s not one of my cats posting a blog entry.

Rather, it’s a whimsical title someone gave to the following composition:

I started my day listening to this. I am still smiling. I think it sounds a little bit like Klingon opera, or perhaps like a piano piece written by a Klingon composer. But it’s not bad, not bad at all.

 Posted by at 3:47 pm

A beautiful photograph

 History  No Responses »
May 132021
 

I was watching a documentary on Netflix and a photo caught my attention. A beautiful, old photograph (shown in color in the documentary, but I suspect it was colorized, so I am including a black-and-white version instead that I found online) showing a young mother and her child, along with a stuffed toy animal:

This photo depicts the sister of Setsuko Thurlow (née Nakamura), a Japanese-Canadian peace activist, herself a survivor of the Hiroshima atomic bomb.

Unfortunately, her sister Ayako was not that lucky. She and her young son Eiji were badly burnt and soon perished.

I get it why the atomic bomb was deemed necessary. With everything I know today, I still would not, could not have made a decision different from that made by Harry Truman back in July, 1945 even if it meant that I could not ever sleep soundly afterwards throughout the remainder of my life. Not with some 10,000 people, most of them civilians, dying in the Pacific theater every day of the war.

Even so… War is horrifying.

Strangely, it’s the toy animal that humanized this picture for me more than anything else.

 Posted by at 10:40 pm

On Modified Gravity

 Personal, Physics  No Responses »
May 132021
 

Last fall, I received an intriguing request: I was asked to respond to an article on the topic of dark matter in an online publication that, I admit, I never heard of previously: Inference: International Review of Science.

But when I looked, I saw that the article in question was written by a scientist with impressive and impeccable credentials (Jean-Pierre Luminet, Director of Research at the CNRS Astrophysics Laboratory in Marseille and the Paris Observatory), and other contributors of the magazine included well-known personalities like Lawrence Krauss or Noam Chomsky.

More importantly, the article in question presented an opportunity to write a response that was not critical but constructive: inform the reader that the concept of modified gravity goes far beyond the so-called MOND paradigm, that it is a rich and vibrant field of theoretical research, and that until and unless dark matter is actually discovered, it remains a worthy pursuit. My goal was not self-promotion: I did not even mention my ongoing collaboration with John Moffat on his modified theory of gravity, MOG/STVG. Rather, it was simply to help dispel the prevailing myth that failures of MOND automatically translate into failures of all efforts to create a viable modified theory of gravitation.

I sent my reply and promptly forgot all about it until last month, when I received another e-mail from this publication: a thank you note letting me know that my reply would be published in the upcoming issue.

And indeed it was, as I was just informed earlier today: My Letter to the Editor, On Modified Gravity.

I am glad in particular that it was so well received by the author of the original article on dark matter.

 Posted by at 4:38 pm

My stepdad

 Personal  No Responses »
May 032021
 

I began writing this last night, when my stepfather Tibor was still alive, albeit just barely.

He passed away this morning after a brief illness, spending his last few nights in a hospital. What began as shortness of breath turned out to be a massive case of pneumonia that now weakened his whole body. At 93 this is not exactly surprising: we don’t live forever and this is how we die.

I decided that I shall not grieve. Instead, I celebrate. I celebrate a life of 93 years, the good life of a good man, who treated me always as though I was his own son.

I celebrate a life that was lived mostly in good health, near perfect health as a matter of fact, except for a few scary moments in the past decade. But he recovered from it all, and up until last week, really, though he had mobility issues, he still looked radiantly healthy, 20 years younger than his true age.

So there will be no 50th wedding anniversary with my Mom in 2024. No 100th birthday party in 2028. So what? The life that he lived is still a very, very good life.

Here are a few pictures.

My Mom and Tibor met in 1974 in the resort that my stepfather managed. This picture is, I believe, from April 1974. The woman standing was the programs manager (“kultúros”) of the resort.

Here’s another, undated picture of Tibor from roughly the same time period:

Tibor and my Mom built a beautiful house in Visegrád. This is Tibor in the living room, around 1990 or so, under a small Christmas tree.

As communism came to an end, it upset the economy in many ways. In his late 50s, Tibor found a new way to earn an income: he bought a pickup truck and offered moving and delivery services.

This was Tibor just last year, when I last saw him in person, a visit to Hungary that now feels miraculous to have happened at all, in the calm before the storm, before the pandemic changed the world:

And now he is gone.

Just yesterday I came across my all time favorite movie quote on Facebook, a quote from Blade Runner:

“All those moments will be lost in time, like tears in rain. Time to die.“

 Posted by at 12:37 pm

Vaccines (not) made in in Canada

 Canada, Health, Politics  No Responses »
Apr 282021
 

The CBC just published a very informative article on the history of vaccine manufacturing in Canada, explaining why this G7 country, one of the top industrialized nations on Earth, is entirely dependent on imports when it comes to COVID-19 vaccinations.

It really is disgraceful. Canada’s Connaught Labs, founded in 1914, was at the forefront of global vaccine production for many decades.

But then came the decline. Vaccine production is not always a profitable enterprise. Connaught Labs was eventually nationalized by Pierre Trudeau’s government but then, as far as I am concerned inexplicably, the emphasis for this now Crown corporation was to turn a profit!

Why???

Eventually, it was reprivatized by Mr. Mulroney, who promised that the action will bring “net benefits” to Canadians.

Yeah, right.

The federal government is now investing serious monies to expand capabilities for future pandemics. I can only hope that this lesson is not going to be forgotten anytime soon.

 Posted by at 11:34 am

Making sense of Trumpism

 Internet, Personal, Politics, Society  No Responses »
Apr 282021
 

So the other day, I made a foolish decision: I objected to a self-described progressive activist’s recurring, disparaging use of the expression, “white people”, on Twitter.

In response, I learned the following, thanks to helpful strangers:

  1. I am suffering from white fragility;
  2. As I am a man, I am suffering from male fragility;
  3. I am wallowing in prejudices;
  4. Even if I am not from the US, there are issues in Canada, too, so…
  5. I am a racist;
  6. I am afraid of being called a racist;
  7. I benefit from systemic racism and need to be educated about it;
  8. And finally, this gem: I should shut up and listen.

OK, just to be clear, I am no more concerned about being called a racist than I am about being called a bicycle, on account of being neither. However, this reaction speaks volumes. In this new, progressive world, virtue signaling is key if you want progressives to like you. Saying disparaging things about white people gets you credit. Extra credit if you yourself happen to be white and practice a little self-loathing in public.

I used to have zero patience for my conservative-leaning white friends and acquaintances who were complaining about “anti-white racism” as they marched off to vote, or otherwise express support, for that stable genius, the Orange Person. But in light of this little Twitter exchange, I am somewhat less incredulous and more sympathetic.

No, I am still not rooting for Trumpists and their fellow travelers in other countries. But I do have a point to make, not that I expect the most vocally self-righteous progressives to listen: If you manage to turn someone like me (I am not exactly a stereotypical raging white supremacist) into a skeptic, do not be surprised if you lose by a landslide in future election cycles. Tone it down please. There is no need to turn into enemies people who dare to criticize excessive rhetoric, who see nuances where you only see black-and-white, who present inconvenient facts even when those being inconvenienced by them are not from the conservative camp. Listen to their criticism, don’t automatically reject their thoughtful objections in self-righteous indignation, in the name of ideological purity.

As for the Twitter exchange, I ended up doing something I do extremely rarely, unfollowing, even blocking some people when the conversation began to veer towards personal insults. (Because, you know, if you run out of thoughtful arguments, name-calling always works. Right.)

 Posted by at 10:58 am

It flies!

 Aviation, History, Space  No Responses »
Apr 192021
 

This morning, a drone took flight. It successfully took off from the ground, hovered for a few seconds, and then landed safely.

What, you ask? How is this supposed to be a big deal? There are millions of drones out there, kids playing with them and whatnot.

Oh, but this drone is special, and not only because it carries a small piece of fabric from the Wright brothers’ very first airplane.

It is special because it flew on Mars.

 Posted by at 11:42 am

Not so glamorous, part 2

 Computer Security, Internet  No Responses »
Apr 172021
 

Yesterday it was hardware, today it was software.

An e-mail that I sent to a bell.ca address was rejected.

Perhaps I am mistaken but I believe that these Bell/Sympatico mailboxes are managed, handled by Yahoo!. And Yahoo! occasionally made my life difficult by either rejecting mail from my server or dropping it in the recipient’s spam folder. I tried to contact them once, but it was hopeless. Never mind that my domain, vttoth.com, is actually a few months older (July 1, 1994 as opposed to January 18, 1995) than Yahoo!’s and has been continuously owned by a single owner. Never mind that my domain was never used to send spam. Never mind that I get plenty of spam from Yahoo! accounts.

Of course you can’t fight city hall. One thing I can do, instead, is to implement one of the protocols Yahoo wants, the DKIM protocol, to authenticate outgoing e-mail, improving its chances of getting accepted.

But setting it up was a bloody nuisance. So many little traps! In the end, I succeeded, but not before resorting to some rather colorful language.

This little tutorial proved immensely helpful, so helpful in fact that I am going to save its contents, just in case:

https://www.web-workers.ch/index.php/2019/10/21/how-to-configure-dkim-spf-dmarc-on-sendmail-for-multiple-domains-on-centos-7/

Very well. It is time to return to more glamorous activities. It’s not like I don’t have things to do.

 Posted by at 2:57 pm
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