HOW TO SOLVE THIS?

[Image Analyst]

I can't read that language but the equation goes in MATLAB exactly as it is written there. That is proper syntax.

[daniel]

Write a function velocity(x,y,z,t) that calculates the instantaneous speed when parameters are given and the following formula is known:

v= sqrt(diff(x).^2+diff(y).^2+diff(z).^2)./diff(t);

Note: The calculation of the function can only be performed when the size of the vectors t,z,y,x have the same size (length).

[Torsten]

function v = velocity(x,y,z,t)
  v = sqrt(diff(x).^2+diff(y).^2+diff(z).^2)./diff(t);
end

Done.

[daniel]

The calculation of the function can only be performed when the size of the vectors t,z,y,x have the same size (length).

[Torsten]

Yes, then supply t,x,y and z as vectors of the same length.

Or check their lengths in the function.

https://de.mathworks.com/matlabcentral/answers/25317-array-dimensions-equivalence-check

[Matt J]

See guidelines for homework help:

https://www.mathworks.com/matlabcentral/answers/8626-how-do-i-get-help-on-homework-questions-on-matlab-answers

[daniel]

[Walter Roberson]

In the case of that error message, the problem is that you had accidentally created a variable named velocity that you are then trying to index. If there is a variable in scope and a function of the same name, MATLAB gives priority to the variable in scope.

Answer 1

[Image Analyst]

Try this:

v = velocity([0, 5.6, 7], [0, 1.1, 2.4], [0, 4, 20], [0, 1, 2])

v = 1×2

6.9692 16.1137

function v = velocity(x,y,z,t)
    v = [];
    if ~isequal(size(x), size(y)) || ~isequal(size(x), size(z)) || ~isequal(size(x), size(t))
        uiwait(errordlg('Sizes do not match'));
        return;
    end
    v = sqrt(diff(x).^2+diff(y).^2+diff(z).^2)./diff(t);
end

[daniel]

[Image Analyst]

You must be running different code. I ran mine right here in answers. Paste your code in here, just like I did, then click the green run triangle.

What does this show if you type it in the command window?

which -all velocity

All you have is the m-file function, right? You don't have a variable called velocity, right?

[daniel]

[daniel]

its working tnks

[Voss]

@daniel: isequal accepts more than two input arguments and returns true if and only if all the inputs are equivalent.

That is, you can replace this:

if ~isequal(size(x), size(y)) || ~isequal(size(x), size(z)) || ~isequal(size(x), size(t))

with this:

if ~isequal(size(x), size(y), size(z), size(t))

Reference: https://www.mathworks.com/help/matlab/ref/isequal.html#d124e801938