Storing a range as a variable

Imagine the start and end values of a range being set from user input. They could be:

a=3;
b=10;

To extract this range from an array, I simply do:

x(a:b);

But I'd like to save this range as one variable in itself, so that I can insert the range easily many places and only have to change it in one place such as:

range=a:b;
x(range);

This gives an error. MatLab will not store the a:b in this manner since : is a string and I thus am mixing strings with numbers. I could convert the a and b into a string with num2str, but then that range cannot be inserted into the x variable.

Is there a way to do this or do I have to manually put together the range with x(a:b) every time?

[Adam]

range = a:b;

is perfectly acceptable syntax. : is an operator here, not a string.

[Stephen23]

"This gives an error."

Not when I try it:

>> a = 3;
>> b = 10;
>> range = a:b
range =
    3    4    5    6    7    8    9   10

See also the earlier question:

https://www.mathworks.com/matlabcentral/answers/384876-how-to-properly-input-a-range-in-a-vector

Answer 1

[Angelo]

x=[0.1:0.1:2];
range=[3:10];
x(range)

[Jan]

See: http://www.mathworks.com/matlabcentral/answers/35676-why-not-use-square-brackets . The additional square brackets waste time only. They are the concatenation operator, but "3:10" is a vector already and nothing is concatenated.

In addition it is worth to consider, that

x(a:b)

is faster than

v = a:b;
x(v)

because in the first case, the index vector a:b is not created explicitly.

Answer 2

[Jan]

What's wrong with

x(a:b)

You really need to store it in one variable?

Range.a = a;
Range.b = b;
x(Range.a : Range.b)

Or:

Range = {a,b};
x(Range{1}:Range{b})

You could write a function also:

GetInterval(x, Range)

function y = GetInterval(x, Range)
y = x(Range{1}:Range{b});
end

But this will be slower and worse to read than the direct and simple:

x(a:b)

Note that Matlab seems to avoid the explicit creation of the index vector a:b to save time in this case, but this is not documented.