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 Jul2 awarded Curious Oct27 comment How to calculate gradient of $x^TAx$ I have some difficulties in understanding the derivations below the row ends with "+ small term" in the equation array, could you give me some hints? Thank you! Oct27 accepted Questions on “painless conjugate gradient”: take gradient of a quadratic form Oct27 comment Questions on “painless conjugate gradient”: take gradient of a quadratic form I really like this flavor of derivation, it is more straightforward and avoids the problems I encountered. Please review the minor fix on one equation in your answer. Thank you. @littleO Thank you very much for other solutions. I am interested in your answer in that Q/A(which seems to solve my first sub-question). I leave a comment in your answer for some details. Oct27 revised Questions on “painless conjugate gradient”: take gradient of a quadratic form Add the missing 1/2 factor to the third term in the right hand side of the equation in the "As a result" paragraph. Oct27 suggested approved edit on Questions on “painless conjugate gradient”: take gradient of a quadratic form Oct27 asked Questions on “painless conjugate gradient”: take gradient of a quadratic form Oct14 accepted Confusion about Monte Carlo integration Sep26 asked Confusion about Monte Carlo integration May24 comment Why can I integrate something like “infinitesimal part” to calculate the length, area, volume, etc.? em....it seems that I did not state my question clearly. Yes, I understand I need to choose different integrand based on different definition of "distance". But further I want to know why a particular integrand(is that so called measure?) can be integrated to get correct length/area/volume. In low dimensions(<=3) and with real life appreciable measure(length/area/volume), the intuition can help me to determine the correct integrand. But in higher dimension or with an "artificial" measure(like probability) I find it very difficult. May23 asked Why can I integrate something like “infinitesimal part” to calculate the length, area, volume, etc.? Feb24 asked The mathematics behind Sobol sequences Nov19 asked Re-calculate solution after altering some elements in a linear system Oct19 asked uncertainty in solving constraint problem Oct14 asked Is it possible to change a piece of curve's interpolation type of a B-Spline via modifying knots? Sep21 awarded Custodian Aug28 accepted Problem in Deducing Perspective Projection Matrix Aug24 revised Problem in Deducing Perspective Projection Matrix added 501 characters in body Aug23 awarded Supporter Aug23 accepted what's the general form of 3D projective mapping?