index must be a positive integer or logical.

I am getting the error : "Attempted to access x(1.01); index must be a positive integer or logical."

Help would be appreciated please :)

clc, clear all func = @(t,x) -t*x;

t = 0; x = 1; h = 0.01; N = 10 tarrays = zeros(1,N); xarrays = zeros(1,N);

for i = 1:h:N

    x(i+1) = x(i) + h.*func(t(i),x(i));
    tarrays = t(i)
    xarrays = x(i+1)
end

[Image Analyst]

http://www.mathworks.com/matlabcentral/answers/13205-tutorial-how-to-format-your-question-with-markup

Answer 1

[Jose]

Got the answer guys

I change the step into a length values of the steps :)

t = 0; %Initial Value
x = 1; %Initial Value
h = 0.1; %Step size
N = 10;
Nvec = [1:h:N];
step = length(Nvec);
tarrays = zeros(1,N)
xarrays = zeros(1,N)

for i = 1:step

Answer 2

[Iain]

The issue is that,

on the second time through the loop, i = 1.01, you need to make i into an integer.

I suggest having, instead of i and "i+1", you replace i with index, and set

 index = (i-1)*1/h

[Jose]

What does this " (i-1)*1/h " thing do? I want my for loop in steps of 0.1 to 10. Thanks for the reply :)

[Cedric Gilbert]

t = 0; x = 1; h = 0.01; N = 10
for i = 1:h:N
x(i+1) = x(i) +...
end

first occurence : x(2) = x(1) + ... second occurence: x(2.01) = x(1.01) + ... third occurence: x(2.02) = x(1.02) + ...

You can't specify a decimal number to index a matrix ! Doing as lain prescribe => x(i/h)

first occurence : x(0.01/0.01) => x(1) second occurence : x(0.02/0.01) => x(2) etc...

or add an other integer index into your loop.

[Image Analyst]

index = (i-1)*1/h won't work. What happens when i equals 1? You can't have indexes with zero or fractional values. Try using a counter or use integer indexes and get the fractional numbers from that.

Answer 3

[Image Analyst]

I don't know exactly what you want to do, but this is closer, though it still doesn't work:

clc;
clear all
func = @(t,x) -t*x;

t = 0; 
x = 1; 
h = 0.01;
N = 10;
tarrays = zeros(1,N/h);
xarrays = zeros(1,N/h);
index = 1;
for i = 1:h:N    
    x(index + 1) = x(index) + h.*func(tarrays(index), i);
    tarrays(index) = t(index)
    xarrays(index) = x(index+1)
    index = index + 1;
end