Daily tweets about real and complex analysis and related topics. From @JohnDCook.
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A Trip from Classical to Abstract Fourier Analysis ams.org/notices/201409/rnoti… [pdf]
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'I place myself in a certain opposition to widespread views on the nature of the mathematical infinite.' -- Georg Cantor
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A historical example of intellectual noblesse oblige, a scholar who saved lives by making navigation more accessible.
johndcook.com/blog/2026/09/2…
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'Fourier-Motzkin elimination is to linear inequalities what Gaussian elimination is to linear equations.' -- Niels Lauritzen
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Applying {div, grad, curl} to a {div, grad, curl}. johndcook.com/blog/2022/12/0…
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The law of haversines is a variation on the law of cosines with better numerical properties, better suited to navigation at sea.
johndcook.com/blog/2026/09/2…
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Let f be a function of n > 1 complex variables. If f is holomorphic on the complement of a point in an open set U, then f extends to a holomorphic function on all of U.
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If K is a compact subset of a Banach space, the closed convex hull of K is compact. -- Mazur
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From tape measures to tensors johndcook.com/blog/2020/09/2…
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If all the roots of a polynomial are real and negative then its coefficients form a strictly log concave sequence.
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If you take the Legendre transform of a convex function twice you get the original function back.
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Evaluating the zeta function at even integers johndcook.com/blog/2022/06/2…
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Rouché's theorem: If f and g are analytic and |f| > |g| along a regular closed curve, then f and f+g have the same number of zeros inside.
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