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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

```

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