Outer Operation

e.g. Outer Product, Outer Sum, Outer Equals etc...

Description

Calculates resultant matrix when the OPERATOR is applied to all combinations of the elements of vector A and the elements of vector B e.g. the outer product of A and B is outerop(A,B,'*'), the outer sum of A and B is outerop(A,B,'+')

If OPERATOR is omitted '+' is assumed

This function is equivalent to the APL language's circle.dot operation. e.g. in APL Ao.*B is the outer product of A and B % and Ao.+B is the outer sum.

Ideally, it would work on matrices but in practice
I've only ever needed to use it with vectors.

• MATLAB release: MATLAB 7 (R14)

[urs (us) schwarz]

nowadays one could replace the switchyard with this more versatile approach

% start of code
% now, instead of comparing all possible ops

     fop=str2func(operator);
     y=fop(outera,outerb);

% eg,
     fop=str2func('+')
% fop=@plus

profiling both versions shows that there is no penalty in speed between the hand-coded and the function-handle code

just a thought
us

[Keith Bonin]

Only works on vectors.

[Zeke Cummings]

I love outerop and suggest it be part of the next MATLAB release. Murphy told me, " it works with any diadic function e.g. like this outerop(1:5, 6:-1:1, 'max')".

[Matthew Dowle]

I only had a quick look. Isn't this going to be slow for large vectors. It does "*ones()" which will repeat the vector over and over again in memory. It does this "*ones()" for both vectors. Isn't this innefficient, it will be slow and use too much memory. Does matlab have an efficient outer() function which does a nested for() loop through the vectors, without bloating them in memory first, and then populate the result matrix, which is the only memory required that large. Does such an efficient function exist?