# Error usin .* Too many output arguments. How to save three variables at the same time in a loop?

1 view (last 30 days)
Igor on 8 Jun 2022
Edited: Stephen23 on 8 Jun 2022
I need to do the following Clarke transform of a three-phase voltage signal, as follows:
I'm having the following problem:
this is the code:
clear all; close all; clc;
N = 32; a = 1;
t = arq(:,1);
Va1 = arq(:,2); Vb1 = arq(:,3); Vc1 = arq(:,4); %tensoes BUS1
Ia1 = arq(:,5); Ib1 = arq(:,6); Ic1 = arq(:,7); %correntes BUS1
% Va2 = arq(:,8); Vb2 = arq(:,9); Vc2 = arq(:,10); %tensoes BUS2
% Ia2 = arq(:,11); Ib2 = arq(:,12); Ic2 = arq(:,13); %correbtes BUS2
Vbeta1=zeros(length(t),3);V01=Vbeta1;Valpha1=V01;
for a = 1:size(t,1)
[V01(a,1) V01(a,2) V01(a,3)] = [1 1 1;2 -1 -1;0 sqrt(3) -sqrt(3)].*[Va1(a);Vb1(a);Vc1(a)];
end
HOW CAN I SOLVE THIS??
##### 2 CommentsShowHide 1 older comment
Igor on 8 Jun 2022
The size are Va1 = [400001,1], the same for Vb1 and Vc1

Stephen23 on 8 Jun 2022
Edited: Stephen23 on 8 Jun 2022
Do not use separate variables with names Va, Vb, Vc, etc. The name MATLAB comes from "MATrix LABoratory". MATLAB is designed to work efficiently and simply with matrices. Your task is perfect for using matrices, rather than lots of separate variables. You should use matrices.
Do not use a loop. The operation you need is very simple matrix multiplication. Using a loop is much more complex.
Vin = rand(7,3); % much better in one matrix, i.e. arq(:,2:4)
M = [1,1,1;2,-1,-1;0,sqrt(3),sqrt(3)];
Vout = M*Vin.'/3
Vout = 3×7
0.3928 0.3785 0.4278 0.6874 0.2438 0.4356 0.3693 0.4709 0.0741 -0.1156 -0.3263 -0.2120 0.0251 0.4612 0.1817 0.3943 0.5607 0.9821 0.4039 0.4885 0.1601
Checking:
1/3 * M * [Vin(1,1);Vin(1,2);Vin(1,3)]
ans = 3×1
0.3928 0.4709 0.1817
Igor on 8 Jun 2022
Perfect!!

the cyclist on 8 Jun 2022
Given the image of the calculation you posted, I think you want matrix multiplication, not elementwise multiplication:
[V01(a,1) V01(a,2) V01(a,3)] = [1 1 1;2 -1 -1;0 sqrt(3) -sqrt(3)]*[Va1(a);Vb1(a);Vc1(a)]
[V01(a,1) V01(a,2) V01(a,3)] = [1 1 1;2 -1 -1;0 sqrt(3) -sqrt(3)].*[Va1(a);Vb1(a);Vc1(a)]
(Note the use of * instead of .*)
See this documentation for array vs matrix operations.
##### 2 CommentsShowHide 1 older comment
Stephen23 on 8 Jun 2022
"Even if the dimensions of Va1, Vb1 and Vc1 are [400001 1]?"
No.
This code contains exactly the same bug as your question, namely trying to return three outputs from an operation which only returns one output. Whether you use array or matrix multiplication makes no difference to that bug.