Length of a 3D curve.

So I have created the code to calculate the length of a 3D curve which is:

function length_total = spacecurvelength(x,y,z,a,b,n)
% x, y and z are the curves
% a=lower limit b=upper limit n = number of straight lines used to approximate the curve length
syms s
N= a:(b-a)/n:b;

xi=subs(x,s,N);
yi=subs(y,s,N);
zi=subs(z,s,N);

length_total=0;
m=length(N);
% there are m-1 splines for m points

for i=1:1:m-1
dx=xi(i+1)-xi(i);
dy= yi(i+1)-yi(i);
dz=zi(i+1)-zi(i);

length_each=sqrt(dx^2+dy^2+dz^2);
length_total=length_total+length_each;

end
end

I am calling it with:

clear;
curvelength = spacecurvelength(@(s) 2*sin(s),3*cos(s)*exp(s),s.^2/10,-4*pi,pi,100)

But I'm getting the error

Undefined function or variable 's'.

Answer 1

[John D'Errico]

Or, you could just use my arclength code which does the arclength computation using either a spline or a piecewise linear approximation when speed is needed.

Answer 2

[Dasharath Gulvady]

You have declared 's' inside "spacecurvelength" function. I am guessing it needs to be declared outside.

>> syms s;
>> curvelength = spacecurvelength(@(s) 2*sin(s),3*cos(s)*exp(s),s.^2/10,-4*pi,pi,100)