Having trouble figuring out how to write a loop, can someone tell me how I can fix my code?

I am trying to determine the time (t) when P(t) will be zero. intially t should be zero, and then go up 1 every time it runs.

x = 10e10;
u = 10e6;
v = 0.04;
t = 0;
P(t) = (x - u * ( 1 + v * t ));
while( P(t) > 0.000000001)
     t = t+1;
    P(t) = (x - u * ( 1 + v * t ));
end
disp (t);

[per isakson]

Matlab index is one-based. Replace

t = 0;

by

t = 1;

[Jason Logston]

Okay, Thank You

Answer 1

[Star Strider]

Being lazy, I would use the fzero function:

P = @(t) (x - u * ( 1 + v * t ));
tz = fzero(P, 1)

[Jason Logston]

Well I have it running now just by setting t = 1, but the answer I am getting is not what I am looking for. I am getting the answer for t if you were just to solve the equation for t. I think the problem is that my x is not updating each time the equation is ran. I kept what I had and added x = P(t) as the last line in my while loop, seems to be a reasonable number. Thank you for the advice though.

[Image Analyst]

Did you see my answer? It uses your while loop, like you wanted, and gives the same answer for t that you'd get by solving the equation: t = 249975, which is also the same as what Star's answer gives. What answer were you expecting?

Answer 2

[Image Analyst]

Try this - make an anonymous function.

x = 10e10;
u = 10e6;
v = 0.04;
t = 0;
P = @(t) (x - u * ( 1 + v * t ));
maxNumIterations = (x/u-1)/v+1;
while (P(t) > 0) && (t <= maxNumIterations)
  fprintf('P(%d) = %f\n', t, P(t));
  t = t + 1;
end
fprintf('P(%d) = %f\n', t, P(t));
plot(0:t, P(0:t), 'b-', 'LineWidth', 2);
grid on;
message = sprintf('t = %d\nP(t) = %f', t, P(t));
helpdlg(message);