This error occurs because of the way that the inline objects are created. The inline object contains strings that are evaluated using the EVAL function to determine the function value. In the example,
f = inline('[2*sin(x) tan(x)*cos(y)]', '[x y]')
the string is:
'[x y] = INLINE_INPUTS_{1};'
"INLINE_INPUTS" will be a cell array (similar to VARARGIN), where each cell element will contain one of the inputs to the inline object. However, MATLAB cannot return multiple object from indexing into an array with a single value, which is why the error occurs.
Instead, the inline object should be defined so that it uses a single variable, and that variable contains multiple elements:
f = inline('[2*sin(x(1)) tan(x(1))*cos(x(2))]', 'x')
Now, when the inline object is passed a single input variable, it will index into that variable to obtain the values.
In addition, if you have a function of a single variable, but you want to use a vector or matrix of values for that variable, you should use the VECTORIZE command on the inline function.
f = inline('x^2 + x + 1');
f = vectorize(f);
f([1 2;3 4])
which results in
ans =
3 7
13 21
