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## Re: Few questions (convolutions, 'mapping', linspace)

**From**: |
John Eaton |

**Subject**: |
Re: Few questions (convolutions, 'mapping', linspace) |

**Date**: |
Mon, 16 May 94 14:14:13 EDT |

address@hidden (Przemek Klosowski) wrote:
: - I often find myself defining a function (y=fun(x)), and hoping to
: be able to 'map' (in the LISP sense) the vectors/matrices with
: this function, for instance to plot it.
Here's one way to do it, but it won't be very fast.
function y = map (f, x)
# Given a function y = f (x) that expects a scalar argument and
# produces a scalar result, call it for each element of the matrix x
# and return the corresponding matrix of values.
if (nargin != 2)
error ("usage: map (f, x)");
endif
if (! isstr (f))
error ("map: expecting string as first argument");
endif
[nr, nc] = size (x);
y = zeros (nr, nc);
for j = 1:nc
for i = 1:nr
y (i, j) = feval (f, x (i, j));
endfor
endfor
endfunction
It might be desirable to add this as a built-in function to speed it
up, but even then it won't be all that fast because it will require
multiple calls to a user-supplied function, which is fairly slow.
jwe

**Few questions (convolutions, 'mapping', linspace)**, *Przemek Klosowski*, `1994/05/16`
**Re: Few questions (convolutions, 'mapping', linspace)**, *John Eaton*, `1994/05/16`
**Re: Few questions (convolutions, 'mapping', linspace)**,
*John Eaton* **<=**
**Re: Few questions (convolutions, 'mapping', linspace)**, *John Eaton*, `1994/05/16`