why does it take forever to generate some matrices in the Matlab gallery?

Question

Viviana Arrigoni 2019-1-28

评论： Viviana Arrigoni 2019-2-1

I interrupted the execution of

gallery('randcorr',n)

and

A = gallery('toeppd',n,n,rand(n,1),rand(n,1));

for n = 10000 after almost one hour. I know my computer is not the fastest, but for other matrices in the gallery, it would take seconds.

Answer 1

Matt J 2019-1-28

编辑：Matt J 2019-1-28

Because some of the matrix types in the gallery are computationally expensive to construct. In particular, in

A = gallery('toeppd',n,n,rand(n,1),rand(n,1));

you are asking for the summation of 10000 matrices, where each matrix is itself 10000 x 10000. That is a lot of number crunching.

double clicked to Accepted and signed as Unaccepted by mistake. Seems like I can't undo that, sorry...