Dear gretl folks greetings from Paris ! A quick reaction to Sven's mail about Sir Roger Penrose, one of the co-authors of the Moore-Penrose generalized inverse, or pseudo inverse. A few words on it on the great mathematica encyclopedia: https://mathworld.wolfram.com/Moore-PenroseMatrixInverse.html Roger Penrose is a great mathematician and theoretical physicist. I think he found the pseudo inverse at a time where computaiton power was at a premium and physicists had to deploy a lot of ingenuity to analyze the spectrum of particle experiments in the context of the Standard Model of particle physics. At the time of the paper by Penrose (1955), was ahead of the discovery of the quark (Murray Gellman, 1964 if I remember well). Interestingly, generalized inverses slowly made their way into statistics and econometrics in the 1970s, at least in french manuals where every authors displayed pseudo inverses in the late 1970s. Roger Penrose wrote great books for the mathematically informed reader, dismissing the inverse squared law of editors stating that every equation divides sales par 2. Penrose non fictions essays display in the hundreds and still sale very well. His point is that even if you dont understand anything to the equation seeing it or reading brings you something however small ! Penrose is also known as a mathematician who contributed among many other things to the typology of euclidiean and non euclidean tessellations. He his famous for this famous Penrose kite tesselation (one of the 15 non periodic tessalations of the eucledean plane). He also invented to very strange and mysterious birdtrack diagrammatic notation of tensors still very useful and unsurpassed in physics: https://en.wikipedia.org/wiki/Penrose_graphical_notation It could be used for group theory and even perhaps some econometric work. A very interesting and creative physicist. All the best folks, regards. Franck. -------- Message original -------- Sujet: [Gretl-users] Penrose Date: Jeudi 8 Octobre 2020 14:58 CEST De: Sven Schreiber <svetosch(a)gmx.net&gt; Répondre à: Gretl list <gretl-users(a)gretlml.univpm.it&gt; Pour: gretl-users(a)gretlml.univpm.it