Plotting several values returned by a function.

Hi, I wrote the following function for the interpolation polynomial of log(x):

function pol = Lagrange1(x)
dim1 = [1, 2, 4];
dim2 = [0, 0.693, 1.386];
pol1 = dim2(1)*(x-dim1(1))*(x-dim1(3))/[(dim1(1)-dim1(2))*(dim1(1)-dim1(3))];
pol2 = dim2(2)*(x-dim1(1))*(x-dim1(3))/[(dim1(2)-dim1(1))*(dim1(2)-dim1(3))];
pol3 = dim2(3)*(x-dim1(1))*(x-dim1(2))/[(dim1(3)-dim1(1))*(dim1(3)-dim1(2))];
pol = pol1 + pol2 + pol3;

I'd like to plot the value it returns for x = 0.01:0.01:12. How may I go about it, please? I have tried using ordinary plot(), in a loop even, to no avail.

Answer 1

[Jie]

You could have plotted the result in a loop (if you have used the function file correctly). But I suggest u not do this.

In order to make this right and simple, change your function file into the following:

function pol = Lagrange1(x)
dim1 = [1, 2, 4];
dim2 = [0, 0.693, 1.386];
pol1 = dim2(1)*(x-dim1(1)).*(x-dim1(3))/[(dim1(1)-dim1(2))*(dim1(1)-dim1(3))];
pol2 = dim2(2)*(x-dim1(1)).*(x-dim1(3))/[(dim1(2)-dim1(1))*(dim1(2)-dim1(3))];
pol3 = dim2(3)*(x-dim1(1)).*(x-dim1(2))/[(dim1(3)-dim1(1))*(dim1(3)-dim1(2))];
pol = pol1 + pol2 + pol3;

only three dots were added. But now your function file is vector/matrix supported.( Your previous file is only scalar supported ) And then use this following code:

x = 0.01:0.01:12;
y=Lagrange1(x);
figure,plot(x,y)

[Yuval]

Great! Thank you so much :)