Number of elements mismatch.

Hi everyone,

I have a dimension issue:

I have a Simulink Matlab Function block that has a [3x1] vector of values called pd as its input. This vector should turn into a [6x1] vector called pdot by adding three zeros to every element. Basically just resizing

from to it sounds rather simple but I can't get it to work. The code that I use in my Simulink function block is shown below.

function pdot = fcn(pd)
pdot = zeros(6,1);
temp = zeros(6,1);
    for i = 1:length(pd)
    pdot(i) = temp(i) + [pd(i); 0; 0; 0];
    end
end

Thanks in advance for any tips or advice.

Answer 1

[Dave B]

This seems like you maybe over complicated it? Is it as simple as...

x=[1;3;5]

x = 3×1

1 3 5

fcn(x)

ans = 6×1

1 3 5 0 0 0

function pdot = fcn(pd)
pdot=[pd;0;0;0];
end

(note that padarray can also be used to do this)

[Mike Leijten]

Thanks. I have a follow up question if you don't mind:

pd is 3x1x51 in the workspace (51 are the timesteps in Simulink) and pdot is 51x6. How can I get pdot to look like 6x1x51?

[Dave B]

Happy to help.

Two options:

Take the 51 x 6 and make it 6 x 1 x 51:

pdot=rand(51,6);
pdot=reshape(pdot.',6,1,51); % transpose then reshape

Use padarray to add the zeros directly to the 3 x 1 x 51:

pd = rand(3,1,51);
pdot = padarray(pd, [3 0 0], 0, 'post'); % pad with 3 rows (0 columns, 0 in third dimension), with the value 0, padding on the 'bottom' not the 'top'