CODEWITHSUNDEEP
matrixprologclpfd
user721588
user721588

Reputation:

matrix multiplication in prolog

I found a code that multiplicates matrixes.

% SWI-Prolog has transpose/2 in its clpfd library
:- use_module(library(clpfd)).

% N is the dot product of lists V1 and V2.
dot(V1, V2, N) :- maplist(product,V1,V2,P), sumlist(P,N).
product(N1,N2,N3) :- N3 is N1*N2.

% Matrix multiplication with matrices represented
% as lists of lists. M3 is the product of M1 and M2
mmult(M1, M2, M3) :- transpose(M2,MT), maplist(mm_helper(MT), M1, M3).
mm_helper(M2, I1, M3) :- maplist(dot(I1), M2, M3).

If I type: mult([[1,2],[3,4]],[[5,6],[7,8]],X). then I get X = [[19, 22], [43, 50]].

But how I can get a X = [[1*5+2*7, 1*6+2*8], [3*5+4*7, 3*6+4*8]] .

P.S. I am new to prolog. Thanks!

Upvotes: 4

Views: 2344

Answers (1)

mat
mat

Reputation: 40768

This is easy: Instead of evaluating the arithmetic expressions with is/2, simply leave them unevaluated and use the compound terms instead of their numerical values. I do it for product/3: Instead of

product(N1,N2,N3) :- N3 is N1*N2.

I write:

product(N1, N2, N1*N2).

You only need to write a corresponding version of sumlist/2.

Upvotes: 7

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