CODEWITHSUNDEEP
matrixvectorlinear-algebramaxima
goshanoob
goshanoob

Reputation: 75

How to get vector from matrix in Maxima

I want to multiply matrix M to vector V. Should be a vector. I write

M:matrix([a,b,c],[d,e,f],[g,h,r]);
V:[w,k,t];
res:M.V;

I get the column-matrix. I want to get list [a*w+c*t+b*k,d*w+f*t+e*k,g*w+r*t+h*k]. OK. I have to write res:[res[1][1],res[2][1],res[3][1]]; How to do it more efficiently?

Upvotes: 1

Views: 2587

Answers (3)

Rax Adaam
Rax Adaam

Reputation: 810

Just adding this, for completeness, in case anyone else has the same question.

First, I believe V, as defined in the OP, is actually a list and not a vector, by Maxima's definitions; however, the approach is the same, in either case:

M:matrix([a,b,c],[d,e,f],[g,h,r]);
V:[w,k,t];                /* V is a list */
v1:transpose([w,k,t]);    /* v1 is a column vector */
v2:matrix([w],[k],[t]);   /* v2 is a column vector */

In all cases, use args:

output1:args(M.V);   /* returns a list of lists */
output2:args(M.v1);  /* returns a row vector */
output3:args(M.v2);  /* returns a row vector */

will return objects that look the same, but don't have exactly the same behaviour. For example:

output1[1,1];   /* will return an error, because `output1` is a list, not a matrix */
output1[1][1];  /* will return the first (only) entry of the first list */

output2[1,1];  /* returns the 1-1 element of the vector `output2` */
output2[1][1]; /* isn't defined, because `output2` is a vector, not a list */

(and similarly for output3).

Upvotes: 0

link
link

Reputation: 11

This function returns the i-th column of a matrix similar to Matlabs M(:,i) 

col(M,i) := 
    block(
        return(transpose(transpose(M)[i])) 
    )$

This function returns the i-th row of a matrix similar to Matlabs M(i,:) 

row(M,i) := 
    block(
        return(transpose(transpose(M[i])))
    )$

Upvotes: 1

Michael
Michael

Reputation: 5335

transpose(res)[1];

-> [a*w+c*t+b*k,d*w+f*t+e*k,g*w+r*t+h*k]

Upvotes: 2

Related Questions