Index in position 2 exceeds array bounds

Hello,

i'm trying to add values to an already existing array (Profile_y). The last value of Profile_x is lager than the last value of Profile_y. I am calculating the difference and divide it by the average step size of the values to get the number of how many steps i need to add. After that i try to add the average stepsize MissingSteps-times to the vector, so that Profile_x and Profile_y should have the same endvalue after all.

Instead i'm getting the error:

Index in position 2 exceeds array bounds

The end operator must be used within an array index expression.

My code:

MissingSteps = floor((Profile_x(1,end) - Profile_y(1,end)) ./ (mean(diff(Profile_y))));
        
Profile_Y_new = [Profile_Y];
% Profile_Y_new(1,end+1:numel(Profile_Y_new) + MissingSteps) = 0;
k = 1;

for i = 1:MissingSteps
    Profile_Y_new(1,end+k) = Profile_Y_new(1,end+k-1) + (mean(diff(Profile_Y)));
    while k <= MissingSteps
        k = k + 1;
    end
end

[LM]

I have encountered this special error message many times before and still don't know, what is wrong with my general approach to loops.

[Walter Roberson]

Which line is the problem occuring on?

What is class(Profile_x) and class(Profile_y) ?

    while k <= MissingSteps
        k = k + 1;
    end

What is the point of that? Why not just do

    k = MissingSteps + 1;

[LM]

I guess you want to know that Profile_x is a 1x100 double and Profile_y is a 1x9000 double.

The line with the error:

Profile_Y_new(1,end+k) = Profile_Y_new(1,end+k-1) + (mean(diff(Profile_Y)));

I am trying to let k go from 1 to MissingSteps. If it reaches MissingSteps it should stop.

[Walter Roberson]

MissingSteps = floor((Profile_x(1,end) - Profile_y(1,end)) ./ (mean(diff(Profile_y))));
        
Profile_Y_new = [Profile_Y];
% Profile_Y_new(1,end+1:numel(Profile_Y_new) + MissingSteps) = 0;
k = 1;

for i = 1:MissingSteps
    Profile_Y_new(1,end+k) = Profile_Y_new(1,end+k-1) + (mean(diff(Profile_Y)));
    if k <= MissingSteps
        k = k + 1;
    else
        break;  %stop when enough has been filled
    end
end

[Walter Roberson]

Use the command

dbstop if error

and run the code. When it stops at that line, please ask it to display

class(Profile_Y_new)
class(Profile_Y)
which end
which mean
which diff

[LM]

I have changed the code as you wrote. It still occurs the same error in the same line. k = 2 in the workspace.

When i use dbstop if error nothing happens.

I am not sure, if i have done this correctly in the command window, but:

class(Profile_Y_new) = 'double'

class(Profile_Y) = 'double'

K>> which end

built-in (C:\Program Files (x86)\toolbox\matlab\lang\end)

K>> which mean

C:\Program Files (x86)\toolbox\matlab\datafun\mean.m

K>> which diff

built-in (C:\Program Files (x86)\toolbox\matlab\datafun\@char\diff) % char method

[Walter Roberson]

Those look okay.

When you are stopped at the error line, please command

Profile_Y_new(1,end+k-1)
(mean(diff(Profile_Y)))
Profile_Y_new(1,end+k) = 12345

and see where the error comes up. If it does not come up at all, try putting in the full line

Profile_Y_new(1,end+k) = Profile_Y_new(1,end+k-1) + (mean(diff(Profile_Y)));

and seeing what happens.

I'm wondering whether you have a syntax error in your program somewhere, an extra end statement, a [ opened that is not closed, something like that.

[LM]

Typing in:

Profile_Y_new(1,end+k-1):

Error: Index in position 2 exceeds array bounds

(mean(diff(Profile_Y))):

Give the correct stepsize.

Profile_Y_new(1,end+k) = 12345:

Add the value at third position after the initial endvalue.

Matlab kind of have a problem with '+k'. How do I solve this?

Answer 1

[Jan]

Profile_Y_new(1,end+k) = Profile_Y_new(1,end+k-1) + (mean(diff(Profile_Y)));

This line must fail, because Profile_Y_new(1,end) is the last element of Profile_Y_new already. Then Profile_Y_new(1,end+k-1) tries to read an element behind the last element.

Remember that " end " is an abbreviation for the length of the concerned dimension. Then reading the element at end+k must fail for k > 0.

I assume you mean:

endIndex = size(Profile_Y_new, 2);
for i = 1:MissingSteps
    Profile_Y_new(1,endIndex + k) = Profile_Y_new(1, endIndex + k - 1) + ...
        (mean(diff(Profile_Y)));    

Now endIndex is fixed before the loop, while the keyword "end" is adjusted dynamically to the current size.

[LM]

Thanks a lot for your help and explanation. The problem is clear now.