How can I pass 2-D meshgridded var into a 3-D matrix?

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Ezz El-din Abdullah 2017-7-21

评论： Ezz El-din Abdullah 2017-7-21

I need to pass X and Y which are 2-D meshgridded matrices into c the 3-D matrix. where k is a constant and zv is a vector.

Here is my try:

for i = 1:M
    c(:,:,i)=exp(1j*k/(2*zv(i))*(X2.^2+Y2.^2));
end

Thanks.

Steven Lord 2017-7-21

Show us the sizes of all of X2, Y2, c, and zv as well as the value of M as they are immediately before you enter the loop.

M is 250

X2 is 250x250

Y2 is 250x250

c is not defined before the loop but I want it to be 3D matrix (250x250x250)

Guillaume 2017-7-21

编辑：Guillaume 2017-7-21

Step 1: permute your vector so that it is along the 3rd dimension:

zv = permute(zv, [3 2 1]);  %if zv is a column vector (M x 1)
%or
zv = permute(zv, [1 3 2]);  %if zv is a row vector (1 x M)

Step 2: No need for loop, use memberwise operation + implicit expansion (if on R2016b or later):

c = exp(1j*k./(2*zv)) .* (X2.^2 + Y2.^2));

If on version < R2016b:

c = bsxfun(@times, exp(1j*k./(2*zv)), (X2.^2 + Y2.^2));

Guillaume 2017-7-21

As I wrote,

If on version < R2016b:

c = bsxfun(@times, exp(1j*k./(2*zv)), (X2.^2 + Y2.^2)); %after the permute

Thank you very much.

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