matlab中coeff的用法?
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matlab中coeff的用法?
matlab中coeff的用法?
matlab中coeff的用法?
三次样条插值
function f=spline331(X,Y,dY,x0)
N=size(X,2);
s0=dY(1); sN=dY(2);
h=zeros(1,N-1);
for i=1:N-1
h(1,i)=X(i+1)-X(i);
end
d(1,1)=6*((Y(1,2)-Y(1,1))/h(1,1)-s0)/h(1,1);
d(N,1)=6*(sN-(Y(1,N)-Y(1,N-1))/h(1,N-1))/h(1,N-1);
for i=2:N-1
d(i,1)=6*((Y(1,i+1)-Y(1,i))/h(1,i)-(Y(1,i)-Y(1,i-1))/h(1,i-1))/(h(1,i)+h(1,i-1));
end
mu=zeros(1,N-1); md=zeros(1,N-1);
md(1,N-1)=1; mu(1,1)=1;
for i=1:N-2
u=h(1,i+1)/(h(1,i)+h(1,i+1)); mu(1,i+1)=u;
md(1,i)=1-u;
end
p(1,1)=2; q(1,1)=mu(1,1)/2;
for i=2:N-1
p(1,i)=2-md(1,i-1)*q(1,i-1); q(1,i)=mu(1,i)/p(1,i);
end
p(1,N)=2-md(1,N-1)*q(1,N-1);
y=zeros(1,N); y(1,1)=d(1)/2;
for i=2:N
y(1,i)=(d(i)-md(1,i-1)*y(1,i-1))/p(1,i);
end
x=zeros(1,N); x(1,N)=y(1,N);
for i=N-1:-1:1
x(1,i)=y(1,i)-q(1,i)*x(1,i+1);
end
M=x;
syms t;
for i=1:N-1
pp(i)=M(i)*(X(i+1)-t)^3/(6*h(i))+M(i+1)*(t-X(i))^3/(6*h(i))+(Y(i)-M(i)*h(i)^2/6)*(X(i+1)-t)/h(i)+(Y(i+1)-M(i+1)*h(i)^2/6)*(t-X(i))/h(i);
pp(i)=simplify(pp(i)); coeff=sym2poly(pp(i));
if length(coeff)~=4
tt=coeff(1:3); coeff(1:4)=0; coeff(2:4)=tt;
end
if x0>=X(i)&x0