how to plot the magnitude of a vector ?

i have a curve ([0:20:50000],x(:,3)) I want to calculate the magnitude of this curve, but i obtain zero. Th curve is attache

index=1;
for i=0:20:50000
 xm=(max(x(:,3))-min(x(:,3)));
  xlm(index)=xm;
 index=index+1;
end

[Adam]

What do you do to calculate magnitude when you obtain zero?

[Azzi Abdelmalek]

What is your definition of magnitude for this signal which is not periodic

[KSSV]

What do you mean by magnitude? Is it that you want to calculate the length of the curve?