Clear Filters
Clear Filters

'Assignment between unlike types is not allowed'

4 views (last 30 days)
This is a code i am trying to write for cubic spline interpolation between 4 points...I want to eventually form and plot the three cubic polynomials, but I am getting the error of ' Assignment between unlike types is not allowed' in line 30 i.e when I am defining S(k) in the last for loop. What is going wrong? Would somebody comment? A, B, C are arrays of the coefficients for the 3 polynomials.
syms x X Y
X = [0 1 2 3]
Y = [0 0.5 2 1.5]
n = length(X)
A = sym('A', [1 n]);
B = sym('B', [1 n-1]);
C = sym('C', [1 n-1]);
H = [];
for i = 1:n-1
H(i) = X(i+1) - X(i);
end
for k = 1:n-2
eqns(k) = H(k)*A(k) + 2*(H(k)+H(k+1))*A(k+1) + H(k+1)*A(k+2) == (Y(k+2)-Y(k+1))/H(k+1)-(Y(k+1)-Y(k))/H(k);
end
%for natural spline
eqns(n-1) = A(1)==0;
eqns(n) = A(n)==0 ;
eqns
S = solve(eqns)
A(1) = S.A1;
A(2) = S.A2; A(3) = S.A3; A(4) = S.A4
for k = 1:n-1
B(k) = Y(k)/H(k) - A(k)*H(k);
C(k) = Y(k+1)/H(k) - A(k+1)*H(k);
end
B
C
hold on
for k = 1:n-1
S(x) = A(k)*(X(k+1)-x)^3/H(k) + A(k+1)*(x-X(k))^3/H(k) + B(k)*(X(k+1)- x) + C(k)*(x - X(k))
fplot(S(x), [X(k) X(k+1)])
end
hold off

Answers (1)

Sahithi Kanumarlapudi
Sahithi Kanumarlapudi on 24 Feb 2021
Hi,
In your code 'S' is a struct with 4 fileds and 'A(k)*(X(k+1)-x)^3/H(k) + A(k+1)*(x-X(k))^3/H(k) + B(k)*(X(k+1)- x) + C(k)*(x - X(k))' is a symbolic expression. You may assign the expression to another filed of S but not to S(x) as 'S' is struct.
Hopen this helps!

Categories

Find more on Interpolation in Help Center and File Exchange

Community Treasure Hunt

Find the treasures in MATLAB Central and discover how the community can help you!

Start Hunting!