I need help with using a while loop

My problem I think is quite simple. But I just cannot get my brain around it.

I'm trying to use a while loop to iterate my code until m = 1.000e-5. But when I execute the code what I get is an infinite loop.

Here is the code:

c1 = 0.1;
v1 = 0.1;
v2 = 1;
p = 0;
m = 0;
while m ~= 1.000e-5
    c1 = c1*v1/v2
    m = c1*0.1
    p = p+1
end

Answer 1

[Paul Hoffrichter]

Looks like you are trying to solve a difference equation. Take a look at what is happening:

c1 = 0.1;
v1 = 0.1;
v2 = 1;
p = 2;
m = 0;
while m ~= 1.000e-5
    c1(p) = c1(p-1)*v1/v2; % ==> c1 = c1 * 0.1 since v1, v2 never change in loop
    m(p-1) = c1(p)*0.1;
    if p > 100 || m(p-1) < 1e-8
       break;
    end
    p = p+1;
end
figure(1), plot(c1), title('c1'), xlim([1 15])
figure(2), plot(m),  title('m'),  xlim([1 15])
c1
m

Output:

c1 =
   0.100000000000000   0.010000000000000   0.001000000000000   0.000100000000000   0.000010000000000   0.000001000000000   0.000000100000000   0.000000010000000
m =
   1.0e-03 *
   1.000000000000000   0.100000000000000   0.010000000000000   0.001000000000000   0.000100000000000   0.000010000000000   0.000001000000000

m is decreasing rapidly. Never compare real numbers for equality or inequality. Remove my if-break statement, and adjust your while-loop accordingly.

[Ikmal Rosli]

oh wow never thought of this. Thanks.

Answer 2

[David Hill]

c1 = 0.1;
v1 = 0.1;
v2 = 1;
p = 0;
m = 1;
while m > 1.000e-5%floating point errors, use >
    c1 = c1*v1/v2
    m = c1*0.1
    p = p+1
end

[Ikmal Rosli]

Hello thank you. Is there a way to get around the floating point error. So that m is exactly equal to 1e-5