Matlab doesn't like my function, why?

Does anyone know what i am doing wrong here. i am trying to plot my amplitudes of my fourier series from 0-15 my bn is only a number when odd which explains my matrix.

Answer 1

[Torsten]

Use elementwise division (./) and multiplication (.*) in the computation of An and B:

https://uk.mathworks.com/help/matlab/matlab_prog/array-vs-matrix-operations.html

Answer 2

[Dyuman Joshi]

The element-wise operators to be used here are ./ and .* (There is .^ in addition), see - Array vs Matrix Operations

Also, while defining the variable C - the letters a, b of An, Bn are supposed to be uppercase, and, n of plot C vs N should be lowercase. MATLAB is case sensitive.

And the syntax of calling plot() is incorrect. Take a look at the documentation page to learn the acceptable syntaxes of the function plot() here - https://in.mathworks.com/help/matlab/ref/plot.html

If you are new to MATLAB, I suggest you take the free MATLAB Onramp tutorial to learn the fundamentals/basics of MATLAB along with the notation/syntax.

[AB29]

Thank you the response. I have modified my answer however now my graph is blank.

Why is that?

[Dyuman Joshi]

You need to directly use n -

n = 1:2:15;
A = 3;
An = (A./(pi.*n)).*(sin(pi*n) - sin(0));
Bn = (-A./(pi.*n)).*(cos(pi*n) - cos(0));

C = sqrt(An.^2 + Bn.^2);

plot(n, C)

[AB29]

Amazing thanks. I am now doing the same with these values (below). However I am struggling to get matlab to recognise that the figures in the square root are negative. From hand calculations i get a1 = 0.569 (rounded) and a2 = 0.546 (rounded). Matlab is way off because it doesn't take into account the minus. Any ideas?

[Dyuman Joshi]

Since sum of squares is positive, thus its sqrt() is also positive.

Please state/share -

> What the expected output is.

> The mathematical formula/expression that you are trying to code for An and Bn.

[Steven Lord]

Since you're computing the sine and cosine of multiples of pi, I'd use the sinpi and cospi functions instead of sin and cos. Or if you're trying to compute degree-based sine and cosine, use sind and cosd instead of trying to convert the angles in degrees to radians manually. As for your last calculation, C, use hypot.

[AB29]

This is what i expected

[Torsten]

C1 = sqrt(0.908^2 + (-0.705)^2)

C1 = 1.1496

C2 = sqrt((-0.281)^2 + (-0.614)^2)

C2 = 0.6752

C3 = sqrt((-0.187)^2 + (-1.26)^2)

C3 = 1.2738

[Dyuman Joshi]

@AB29, the signs should be positive, as squaring a negative value results in a positive value.

[AB29]

Thanks all.