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Asked by Cong Bang Huynh
on 12 Jan 2013

Hi all!

I have currently written this code to calculate the radial distance for all points with their x, y and z coordinates.

for x = xmin:step:xmax for y = ymin:step:ymax for z = zmin:step:zmax r((x-xmin)/step+1,(y-ymin)/step+1,(z-zmin)/step+1) = sqrt(x^2 + y^2 + z^2);

end end end

I am wondering if there is a way to vectorize this code so that I don't have to run the nested loops and hence speed up my calculation time, because I have to run the code for quite a number of times to analyze different data sets.

I am new to matlab so this question may seem quite trivial but please do help me :) Thank you in advance.

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Answer by Matt J
on 12 Jan 2013

Accepted answer

x = (xmin:step:xmax).'; y = ymin:step:ymax; z = reshape(zmin:step:zmax,1,1,[]);

r=sqrt(bsxfun(@plus, bsxfun(@plus,x.^2,y.^2),z.^2 ));

Answer by Roger Stafford
on 12 Jan 2013

You can also do:

[X,Y,Z] = ndgrid(xmin:step:xmax,ymin:step:ymax,zmin:step:zmax); r = sqrt(X.^2+Y.^2+Z.^2);

## 1 Comment

## Roger Stafford

Direct link to this comment:http://www.mathworks.com/matlabcentral/answers/58619#comment_122212

Aside from the question of vectorizing code, it is unwise to set up for-loops in the way you show here. The problem is that expressions such as (x-xmin)/step+1 used as indices may not turn out to be exact positive integers due to tiny round-off errors and thereby would produce error messages. For example, with xmin = 0, step = 0.1, and xmax = 1, my machine produces a non-integer for (x-xmin)/step+1 at the seventh step and would complain if I used it as an index. With for-loops you should instead do something like the following so that you are guaranteed to have integer values for your indices: