Plot for Cubic Splines

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Bhavik
Bhavik 2012-10-20
I have created a code which works out the coefficients of each spline but I am having trouble plotting a graph using the coefficients. Matlab has problems recognising arrays like a(k) when using it to plot graphs. I don't know how to overcome this problem and have been trying for a while now.
I used the Burden and Faires, Numerical Analysis book to create the Matlab code.
Heres the code:
x=[1,2,3];
y=[2,3,5];
n = length(x);
for i=1:n-1
h(i) = x(i+1) - x(i);
end
for i=2:n-1
al(i)=((3/h(i))*(y(i+1)-y(i)))-((3/h(i-1))*(y(i)-y(i-1)));
end
l(1)=1;
m(1)=0;
z(1)=0;
for i=2:n-1
l(i)=(2*(x(i+1)-x(i-1)))-(h(i-1)*m(i-1));
m(i)=h(i)/l(i);
z(i)=(al(i)-h(i-1)*z(i-1))/l(i);
end
l(n)=1;
z(n)=0;
c(n)=0;
for j=n-1:-1:1
c(j)=z(j)-(m(j)*c(j+1));
b(j)=(y(j+1)-y(j))/h(j)-(h(j)*(c(j+1)+2*c(j)))/3;
d(j)=(c(j+1)-c(j))/(3*h(j));
end
for i=1:n-1
a(i)=y(i);
end
p=x;
*for k=1:n-1
fplot('a(k)+(b(k)*(x-p(k)))+(c(k)*(x-p(k)).^2)+(d(k)*(x-p(k)).^3)',[p(k),p(k+1)])
hold on
end*
I'm having problems with the last for loop.

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采纳的回答

Matt J
Matt J 2012-10-20
for k=1:n-1
fun=@(x) a(k)+(b(k)*(x-p(k)))+(c(k)*(x-p(k)).^2)+(d(k)*(x-p(k)).^3) ;
fplot(fun,[p(k),p(k+1)])
hold on
end
  2 个评论
Bhavik
Bhavik 2012-10-21
The hold on function isn't working properly. I'm only getting a plot of the last function. I don't get the plots of the function between x = 1 and x = 2
Matt J
Matt J 2012-10-22
No, the code is working fine. Add this as the very last line, if you want to see the entire plot:
axis auto

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