Storing x and y values

Essentially I have a loop as follows:

for i=0:0.5:n

dydx=-47*y+t^3;

y=y+dydx*h;

x=x+h;

end

At each iteration of the loop I would like to store the x and y values that I calculate in a vector, so that I can plot it later on. How would I do this? I tried to add y(i)=y and x(i)=x and I just get back an error warning.

Answer 1

[Image Analyst]

When you first enter the loop and get to this line:

dydx=-47*y+t^3;

can you tell us exactly what is y and t at that point?

Perhaps you want something like this but I have no idea:

numPoints = 20;
% Create initial sample data.
x = sort(rand(1, numPoints), 'ascend')
y = sort(rand(1, numPoints), 'ascend')
t = rand(1, numPoints);
h = 5; % Whatever.
for k = 1 : length(y)
    dydx = -47*y(k) + t(k) ^3;
    y(k) = y(k) + dydx * h;
    x(k) = x(k) + h;
end
plot(x, y, 'b.-', 'LineWidth', 2, 'MarkerSize', 20);
grid on;

[Jordan Shook]

At this point y is initially equal to 1 and for t I am integrating from 0 to 3 with step size of 0.5

[Jordan Shook]

The issue with this is that when I put all the varibles in the format of "y(k)" and "x(k)" I continue to come back with errors

[Image Analyst]

I don't get any errors. And I can't run your code since you only gave a small snippet which gives an entirely different error than what you're asking about. How can we run your code and see the error you have? Hint: read this link.

[Jordan Shook]

Here is my whole code:

Essentially I am trying to use Eulers method to get t and y values that I will plot on an x,y graph. I have changed the numbers because this is a school assignement, and although I am not asking for my code to be written, simply just how to store varibles, I would like to make sure that the assignment does not match.

%% Problem 3

%part a euler

t0=1;

tf=5;

y=1;

h=0.5;

n=(tf-t0)/h;

for i=0:0.3:n

dydt=-7*y+t^3;

y=y+dydt*h;

t=t+h;

end

[Image Analyst]

OK, well then you need to index y and y if you want them to change. Use y(i) = ... and t(i) = .....