Matlab programming error - matlab

Question

I am trying out the questions in programming assignment of Coursera course on Matlab programming as an exercise. This is for my self-study.
Question:
Write a function called classify that takes one input argument x. That
argument will have no more than two dimensions. If x is an empty
matrix, the function returns -1. If x is a scalar, it returns 0. If x
is a vector, it returns 1. Finally, if x is none of these, it returns
2. Do not use the built-in functions isempty, isscalar, or isvector.
My code snippet:
function num = classify(x)
num = -1;
if(x == 3.14159265358979)
num = 0;
elseif(size(x, 2) == 3)
num = -1;
end
end
I got the below result on Matlab.
Problem 4 (classify):
Feedback: Your function performed correctly for argument(s) []
Feedback: Your function performed correctly for argument(s) zeros(1,0)
Feedback: Your function performed correctly for argument(s) zeros(0,4)
Feedback: Your function performed correctly for argument(s) 3.14159265358979
Feedback: Your function made an error for argument(s) [1 2 3]
Am I doing something wrong for arguments [1 2 3]?

Answer 1

If all you want is the code, I'll provide you with the answer, but I suggest you sit down and try to understand how and why this codes solves the problem, I'm guessing you want to learn something from it. Well, here's the code:
function [num] = classify(x)
if numel(x) == 0
num = -1;
return
end
num = sum(size(x) > 1);
end

Answer 2

You can most easily check if x is empty or a scalar by counting the number of elements (i.e. use the numel function). Then to determine if it is a vector or a higher dimensional matrix you need to check if the number of dimensions is less than 3 (this is because ndims returns 2 for both 1D and 2D matrices) and also verify that at least one of the first two dimensions has a size of 1:
function num = classify(x)
n = numel(x);
if n < 2
num = n-1;
else
if ndims(x) < 3 && any(size(x) == 1)
num = 1;
else
num = 2;
end
end
end

Answer 3

You should aim to write a generic function, your function would not work for example for any scalar input than pi.
Use the size function to determine the dimensions of the input, for example:
>> size([])
ans = 0 0
>> size(5)
ans = 1 1
>> size([5 6 7])
ans = 1 3
>> size([5;6;7])
ans = 3 1
Based on this, your function could looke like this:
function [num] = classify(x)
s = size(x);
if s == [0 0]
num = -1;
elseif s == [1 1]
num = 0;
elseif sort(s) == [1 3]
num = 1;
else
num = 2;
end
end

Answer 4

Yes, you tring to compare an array with a float.
It allows to do that (programaticalyl wrong) thing for [] because the array is empty
And for zeros, because the array is empty again: in the first case 0 columns, and in the second 0 rows

Answer 5

function i=classify(x)
[m, n]=size(x);
if n==1 && m==1
i=0;
elseif (m==0 && n==0)|| (m>=1 && n==0) || (m==0 && n>=1)
i=-1;
elseif (n>=1 && m==1) || (n==1 && m>=1)
i=1;
else i=2;
end

Answer 6

function y=classify(x)
[a b]=size(x);
%check for empty matrix
% Do not forget that an empty matrix can be size a x 0 or 0x a, where a can be
% arbitrary number
if (a>0)&&(b==0)||(a==0)&&(b>0)||(a==0)&&(b==0)
y=(-1);
%check for scalar
elseif (a==1)&&(b==1)
y=0;
%check for vector
elseif (a>=1)&&(b==1)||(a==1)&&(b>=1)
y=1;
%other case
else
y=2;
end