How to code the linear Splines function?

Hi all, I am getting stuck with the code of linear Splines function. The error is: "Unable to perform assignment because the indices on the left side are not compatible with the size of the right side" I appreciate for any help. Thanks!

if true
  % code
function out=LSplines(x,pointx,pointy)
n=length(pointx);
for i=2:n
 t1(i)= (pointx(i)-x);
 b1(i)= (pointx(i)-pointx(i-1));
 t2(i)= (x-pointx(i-1));
 b2(i)= (pointx(i)-pointx(i-1));
end
P==0;
for i=2:n
  P(i)= P(i)+pointy(i-1)*t1(i)/b1(i)+pointy(i)*t2(i)/b2(i)
end
end
end

Answer 1

[madhan ravi]

function out=LSplines(x,pointx,pointy)
n=length(pointx);
for i=2:n
 t1(i)= (pointx(i)-x);
 b1(i)= (pointx(i)-pointx(i-1));
 t2(i)= (x-pointx(i-1));
 b2(i)= (pointx(i)-pointx(i-1));
end
P=cell(1,n);
P{1}=0;
for i=2:n
  P{i}= P{i-1}+pointy(i-1)*t1(i)/b1(i)+pointy(i)*t2(i)/b2(i);
end
out=P;
end

[Ni Su]

Thank you! Madhan, Still having error, "Error in LSplines (line 5)

t1(i)= (pointx(i)-x);" This part cause to be incompatible of right and left side.

[madhan ravi]

provide your datas

[Ni Su]

Data is: Write a Mat lab function which will take in n data points and an x value and produce the y value corresponding to the linear spline approximation. Plot the linear spline through the points:(-2,1),(-1.5,3),(-1,0),(-0.5,2),(0,3),(0.5,2),(1,-4),(1.5,7),(2,-1). Thank you!

madhan ravi's reply: so what's x , pointx and pointy in your function?

[Ni Su]

[Ni Su]

pointx: is a vector of x value through the given points:[-2 -1.5 -1 -0.5 0 0.5 1 1.5 2],and same for pointy:[1 -3 0 2 3 2 -4 7 -1],

madhan ravi's reply : what's x?

[Ni Su]

x is the values that we use to plot it out (help the line smoother): for example:x=[-3:0.01:3], and y is the corresponding values of x with the Splines function.

[Ni Su]

this code is working, some issues happen when I try to plot it out.

   function P=LSplines(x,pointx,pointy)
n=length(pointx);
P=cell(1,n);
P{1}=0;
for i=2:n
  P{i}= P{i-1}+pointy(i-1)*(pointx(i)-x)/(pointx(i)-pointx(i-1))+pointy(i)*(x-pointx(i-1))/(pointx(i)-pointx(i-1));
end
end

[Ni Su]

The main code to plot out and the error is:"Invalid data argument"

if true
  %Maincode
pointx = input('Enter the vector of x points: \n');
pointy = input('Enter the vector of y points: \n');
x = [min(pointx)-1:0.1:max(pointx)+1];
y = LSplines(x,pointx,pointy);
plot(pointx,pointy,'r*');
hold on
plot(x,y,'b')
end