How to find minimum from an array in Octave? - arrays

Question

I am a complete beginner at Octave!
I am struggling to figure out the minimum value from the array mse_array. I keep getting an error saying: "subscript indices must be either positive integers less than 2^31 or logicals"
Could someone help me? Here's my code:
function randomLines(data1, data2)
mse_array = []
A = rand(2,10)*100
for i = columns(A)
max = A (1, i)
min = A (2, i)
m = (max-min)/0.16
p = [m min];
array_function_values = polyval(p,data2);
current_mse = mseFunction(data1,array_function_values);
mse_array(end + 1) = current_mse
endfor
min_value = min(mse_array)
endfunction

Answer 1

Q: How to find a minimum from an array in Octave?
octave has built-in self-describing documentation to use once in doubts
A: Always re-read both help min and doc min
octave-3.2.4.exe:1> help min
`min' is a function from the file C:\Octave\3.2.4_gcc-4.4.0\libexec\octave\3.2.4\oct\i686-pc-mingw32\max.oct
-- Loadable Function: min (X)
-- Loadable Function: min (X, Y)
-- Loadable Function: min (X, Y, DIM)
-- Loadable Function: [W, IW] = min (X)
For a vector argument, return the minimum value. For a matrix
argument, return the minimum value from each column, as a row
vector, or over the dimension DIM if defined. For two matrices
(or a matrix and scalar), return the pair-wise minimum. Thus,
min (min (X))
returns the smallest element of X, and
min (2:5, pi)
=> 2.0000 3.0000 3.1416 3.1416
compares each element of the range `2:5' with `pi', and returns a
row vector of the minimum values.
For complex arguments, the magnitude of the elements are used for
comparison.
If called with one input and two output arguments, `min' also
returns the first index of the minimum value(s). Thus,
[x, ix] = min ([1, 3, 0, 2, 0])
=> x = 0
ix = 3
See also: max, cummin, cummax
Re-defining (thus rendering un-usable) elements as reserved words just increases troubles. Try to use your own naming convention, that will not harm the rest of the system -- i.e. anArrayMinimumVALUE or aSmallestVALUE, rather than "killing" the Octave function min() by creating a variable named by accident as "also" min

Answer 2

There are several things wrong with your code. Here are a few to get you started.
The error is probably occurring at this line:
min_value = min(mse_array)
You're using mse_array as an index into min, but the values in mse_array are likely to valid array indices as the error states. (I'm guessing at this purely based on the name of the variable, mse_array, which appear to be from some form of mean squared error calculation.) It's important to check the line number and everything else in error messages.
Another issue in that your for loop only evaluates once. The columns function will return the scalar number of columns of A. Thus your your loop declaration is equivalent to:
for i = 10
In other words, the code will only look at the last column of A. You probably want to use:
for i = 1:columns(A)
Lastly, it's a bad idea to overwrite the built-in min and max functions in Octave with your own variable names. If you overwrite the built-in min function, you won't be able to use it anymore directly until you call clear min (alternatively, you can call builtin, but you should avoid that). Instead, just choose better variable names.