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need help vectorizing a complicated loop

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supernoob
supernoob el 17 de Dic. de 2018
Editada: Stephen23 el 19 de Dic. de 2018
Hi,
I need to evaluate a vector of a function on a mesh then sum that vector at each point on the mesh. Let me elaborate:
I have a mesh:
a = -0.5:0.001:0.5;
b = a;
[A,B]=meshgrid(a,b);
At each point on that mesh, I want to evaluate a function over a vector (here, instead of giving the vector values I'm just trying to indicate that I have some vectors with some length):
% I have 3 vectors of length 2000 with some data in them
s = 2000x1 double, c = 2000x1 double, y = 2000x1 double
%at each point A,B on grid evaluate:
fake_function_vec = (c.*A+s.*B-y).^2
%result is some vector of length 2000. Now sum that vector
fake_function = sen(fake_function_vec,1)
%repeat for every other point on the mesh
I can't figure out how to do this efficiently. I'm currently using two for loops to evaluate the function (which returns a vector) and summing that vector at each point in the grid. Surely there must be a better way!
  1 comentario
supernoob
supernoob el 17 de Dic. de 2018
Another option is to use one for loop to evaluate each matrix element on the mesh then sum the stacked matrices. This is also slow.

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Stephen23
Stephen23 el 17 de Dic. de 2018
Editada: Stephen23 el 19 de Dic. de 2018
If you change the size of the s, c and y vectors to 1x1x2000 then this is easy. For MATLAB version R2016b or later:
s = rand(1,1,2000);
c = rand(1,1,2000);
y = rand(1,1,2000);
M = sum((c.*A+s.*B-y).^2,3)
For MATLAB versions prior to R2016b use bsxfun to replace the arithmetic operators.
  1 comentario
supernoob
supernoob el 19 de Dic. de 2018
Thanks so much! Unfortunately this took it from 30s per evaluation to 70s, which really surprised me.

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