linear-algebra

来源： https://stackoverflow.com/questions/27390049/graphics-row-vs-column-major-transformations

来源： https://stackoverflow.com/questions/63631639/floating-point-accuracy-and-order-of-operations

来源： https://stackoverflow.com/questions/63631639/floating-point-accuracy-and-order-of-operations

来源： https://stackoverflow.com/questions/62946604/fitting-a-uniform-grid-to-coordinates-with-random-errors

来源： https://stackoverflow.com/questions/62946604/fitting-a-uniform-grid-to-coordinates-with-random-errors

问题 This question is a follow up to the discussion from this answer. What is the difference between using c(... %*% ...) and sum(... * ...) in a group_by() function from dplyr ? Both of these code give the same result: #1 library(dplyr) # 1.0.0 library(tidyr) df1 %>% group_by(Date, Market) %>% group_by(Revenue = c(Quantity %*% Price), TotalCost = c(Quantity %*% Cost), Product, .add = TRUE) %>% summarise(Sold = sum(Quantity)) %>% pivot_wider(names_from = Product, values_from = Sold) #2 library

问题 This question is a follow up to the discussion from this answer. What is the difference between using c(... %*% ...) and sum(... * ...) in a group_by() function from dplyr ? Both of these code give the same result: #1 library(dplyr) # 1.0.0 library(tidyr) df1 %>% group_by(Date, Market) %>% group_by(Revenue = c(Quantity %*% Price), TotalCost = c(Quantity %*% Cost), Product, .add = TRUE) %>% summarise(Sold = sum(Quantity)) %>% pivot_wider(names_from = Product, values_from = Sold) #2 library

问题 Haven't been able to find any information on this. If I have two m x n matrices of identical dimension, is there a way to apply an element-wise function in numpty on them? To illustrate my meaning: Custom function is F(x,y) First Matrix: array([[ a, b], [ c, d], [ e, f]]) Second Matrix: array([[ g, h], [ i, j], [ k, l]]) Is there a way to use the above two matrices in numpy to get the desired output below array([[ F(a,g), F(b,h)], [ F(c,i), F(d,j)], [ F(e,k), F(f,l)]]) I know I could just do

问题 I am looking for acknowledgement on my perception of a method regarding determining whether a point is located inside a triangle or not in 3D. Given a ray in the form R(t) = e + td and a set of three points T = {V0, V1, V2} that forms a triangle in three dimensions, I know how to find the parametic equation for the plane that the three points form and how to determine if the ray intersects this plane or not. Lastly, if it intersects, I want to know if the intersection point actually is within

问题 The bounty expires in 5 days . Answers to this question are eligible for a +50 reputation bounty. Charlie wants to draw more attention to this question. Based off this question and solution -- Implementing the Bartels–Stewart algorithm in Eigen3? -- I am trying to solve Lyapunov equations (AX + XA^T = C) using the Eigen library, but am limited to real matrices. The R (with c++) code below works, but involves complex numbers. It can definitely be simplified (since in this framing, there is no