I have a problem where I want to set values in a 2D array based on conditions I’ve established. The variables are the NA of the system, its wavelength and the correct units on the device I’m modeling. Using these variables I define a variable N. I set up a 512 by 512 array [x,y]. Then I set up a radius , r = x^2 +y^2 and ask it to give me all r’s(to the closest integer) <= N(the variable I’ve defined above). This gives all the index values in that radius and then I set all those locations to a value of 1. After this I do some FFT ‘s, etc. So how do I do this in Numerical Python without having to index through i,j steps which would be incredibly tedious. This works fairly well in MatLab but I want to port my program to Python(for lots of reasons). If you’d rather I write the MatLab code snippet I can do that. Thanks.

Cliff Martin

One way should be something like this (I haven't tested this) This only works in numarray. If data is the 2-d array where you want to set values within a radius of N (of x0, y0 I presume) y, x = indices(data.shape) data[nonzero(((x-x0)**2+(y-y0)**2) < N**2)] = 1 (in a future version of numarray this will also work and the meaning should be clearer: data[where(((x-x0)**2+(y-y0)**2) < N**2)] = 1 It's a little more involved for Numeric but still possible to do without resorting to loops (I'll leave it to someone else to show that). Does this do what you wanted? Perry Greenfield.

On Wed, 2003-05-21 at 11:08, Cliff Martin wrote:

Hi,

I have a problem where I want to set values in a 2D array based on conditions I’ve established. The variables are the NA of the system, its wavelength and the correct units on the device I’m modeling. Using these variables I define a variable N. I set up a 512 by 512 array [x,y]. Then I set up a radius , r = x^2 +y^2 and ask it to give me all r’s(to the closest integer) <= N(the variable I’ve defined above). This gives all the index values in that radius and then I set all those locations to a value of 1. After this I do some FFT ‘s, etc. So how do I do this in Numerical Python without having to index through i,j steps which would be incredibly tedious. This works fairly well in MatLab but I want to port my program to Python(for lots of reasons). If you’d rather I write the MatLab code snippet I can do that. Thanks.

Cliff Martin

I think part of your code looks like this: x,y = Numeric.indices((512,512)) r = x**2 + y**2 c = r < N In numarray you can then say: a[ c ] = 1 In Numeric, I think you say: a = a.flat c = c.flat Numeric.put(a, Numeric.nonzero(c), 1) a.shape = (512,512) Todd