Can I construct a matrix multiplying a scalar and a vector?

I have a scalar i=3 and a vector j=[4; 5]. I want to generate the matrix k=[3 4; 3 5].

Is there a way to multiply i and j to generate the matrix k?

Answer 1

[Jan]

No, tis is not a standard multiplication. But you can create k based on i and j:

i = 3;
j = [4; 5];

% Solution 1:
k(:, 2) = j;
k(:, 1) = i;

% Solution 2:
k = i .* [1, 0; 1, 0] + j .* [0, 1; 0, 1];   % Auto-expanding, need Matlab >= R2016b

What is the general case? Why do you want a "multiplication"? Which is the problem you want to solve actually?

[Jaime De La Mota Sanchis]

This is my current code. I am trying to construct a Smolyak collocation matrix. This general case is the construction of two rows of said matrix. If you are curious, this is the code I am using.

close all 
clear
clc

contador=1;
number_of_rv=2;


mat_index = ones(number_of_rv+1, number_of_rv);
mat_ampl = zeros(2*number_of_rv+1, number_of_rv);
longitud_mat_ampl=length(mat_ampl);

for i=2: number_of_rv+1
    mat_index(i,contador)=2;
    contador=contador+1;
end

matriz_rv_1_ejemplo= -1*[7 8 9; 0 10 11; 0 0 12];
matriz_rv_2_ejemplo= -1*[1 2 3; 0 4 5; 0 0 6];
matriz_rvs=cat(3,matriz_rv_1_ejemplo, matriz_rv_2_ejemplo);

for i=1: number_of_rv+1
    vector_indices=mat_index(i,:);
    nodes_1=matriz_rv_1_ejemplo(1:vector_indices(1), vector_indices(1))
    nodes_2=matriz_rv_2_ejemplo(1:vector_indices(2), vector_indices(2))
end