如何用Octave绘制3个变量的函数？

Question

I am new to Octave (and matlab for that matter). I have a function that looks like this

I would like to plot g(x,0.5,5) say.

Here it is what I tried in Octave

I defined an anonymous function

f=@(n,x,t) 1./n.*log(n.*pi.*t).*sin(n.*pi.*x);

then another anonymous function

g=@(m,x,t)x.^2+sum(f([1:m],x,t));

Finally defined

x=-1:0.1:1;
plot(x,g(5,x,0.5))

but I get an error. Is this the right way of plotting this function? I must be doing a simple beginner error?

Answer 1

When you call f(n,x,t) , you are passing a 1-by-5 vector for n and a 1-by-21 vector for x . These have different numbers of elements, and therefore can't be multiplied element-by-element. However, you can rewrite f to accommodate vectors for each and perform the sum from g by using matrix multiplication:

f = @(n, x, t) (1./n.*log(n.*pi.*t))*sin(pi.*n(:)*x);
g = @(m, x, t) x.^2 + f(1:m, x, t);

And now your plot will work:

x = -1:0.1:1;
plot(x, g(5, x, 0.5));