need plot a graph using Euler's method for both numerical and analytical
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% Euler's Method
% Initial conditions and setup
h = (10); % step size
x = (0):h:(60); % the range of x
y = zeros(size(x)); % allocate the result y
y(1) = (2); % the initial y value
n = numel(y); % the number of y values
for i=1:n-1
pi = 3.1416
a = 2
r = 1
f = a + (2 - 0.4*a) * x / r^2 * pi
y(i+1) = y(i) + h * f;
end
plot (x,y,'b')
grid on
4 Comments
Jan
on 30 Oct 2022
@Mpho Mokgotlo: If you mention an error, post a copy of the complete error message. Seeing some parts of the message only is less useful, e.g. the readers do not know, in which line the error occurs.
Answers (2)
Alan Stevens
on 30 Oct 2022
Edited: Jan
on 30 Oct 2022
f = a + (2 - 0.4*a) * x(i) / r^2 * pi; % x(i) not just x.
% Also take note of the other comments above.
1 Comment
Jan
on 30 Oct 2022
h = 10; % step size
x = 0:h:60; % the range of x
y = zeros(size(x)); % allocate the result y
y(1) = 2; % the initial y value
n = numel(y); % the number of y values
a = 2;
r = 1;
for i = 1:n-1
f = a + (2 - 0.4 * a) * x(i) / r^2 * pi;
% ^^^
y(i+1) = y(i) + h * f; % I guess this line fails
end
plot (x,y,'b')
grid on
A cleaned version of your code. Alan Stevens' hint is included (please accept his answer).
You can solve such problems using the debugger. Type in the command window:
dbstop if error
and run the code again. Matlab stops at the problem and you can check the values of the used variables.
size(y(i+1)) % A scalar, of course
size(y(i) + h * f) % Not a scalar
size(f) % Same size as x!
You do not want x in the line to get the value of f, but only the element x(i).
Do you really mean: ... / r^2 * pi or .../ (r^2 * pi) ?
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