Euler Method function creation

My homework asks me to:

Write a function [X,Y]=eulermethod(fprime, timespan, y0, h=0.1) where

fprime: function handle representing derivative of f for a given value of x.

timespan=[x0 xend]: starting and ending values of x

y0: f(x0), value of function at x=x0.

h: step size (default h=0.1)

Your function should calculate using Euler's method and store in Y, the successive values of f(x) for X=x0..xend. It is okay if the last entry in X does not reach exactly xend.

Use the eulermethod() function you wrote to approximate the value of sin(x), for x=0..10. Compare the values of sin(x) and the approximated values by showing them on the same plot. What is the average absolute error in your approximated values (average for entire x=0..10, not just for x=10)?

---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- The function that I currently have is:

function [X,Y] = eulermethod(fprime, timespan, y0, h)

if nargin<4, error('at least 4 input arguments required'), end

X_low = timespan(1);

X_high = timespan(2);

if ~ (X_high>X_low), error('upper limit must be greater than lower limit'), end

X = (X_low:h:X_high)';

n = length(X);

if X(n)<X_high

    X(n+1) = X_high;
    n = n+1;
    X(n)=X_high;
end
Y = y0*ones(n,1);

for i = 1:n-1

    Y(i+1) = Y(i) + fprime(X(i),Y(i))*(X(i+1)-X(i));

end

--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- However, when I try to run the function in the MATLAB command using

eulermethod (sin(X), [0,10],10, .1)

I get an error saying

 "Subscript indices must either be real positive integers or logicals"

and

 "Error in eulermethod (line 18) Y(i+1) = Y(i) + fprime(X(i),Y(i))*(X(i+1)-X(i));"

Can you please help me correct this error? I have tried changing the y0 value and the error still exists. Thank you!

[Andrew Newell]

You entered sin(X) for some unspecified value of X instead of a function handle, for example:

eulermethod (@sin, [0,10],10, .1)

However, that's not right either, because they ask for the derivative of sin, which is ...?

[James Tursa]

In addition, OP will need a custom function handle that takes two inputs (current values of X and Y) based on how "fprime" is being used in the code.