typecast to single in MATLAB

What does this call to typecast do in MATLAB?

y=typecast(x,'single');

what does it mean? When I run typecast(3,'single') it gives 0 2.1250.

I don't understand what that is.

I am trying to convert this to Java, how can I do that?

From the MATLAB manual:

single - Convert to single precision

Syntax

B = single(A)

Description

B = single(A) converts the matrix A to single precision, returning that value in B. A can be any numeric object (such as a double). If A is already single precision, single has no effect. Si开发者_如何转开发ngle-precision quantities require less storage than double-precision quantities, but have less precision and a smaller range.

typecast reinterprets the bytes used to represent a value of one type as if those same bytes were representing a different type. For example, the constant 3 in MATLAB is an IEEE double-precision value, meaning it takes 8 bytes to store it. Those eight bytes in this case are

40 08 00 00 00 00 00 00

A value of type single in MATLAB is an IEEE single-precision value, meaning it takes only 4 bytes to store it. So the eight bytes of the double will map to two 4-byte singles, those being

40 08 00 00, and
00 00 00 00

It turns out that 40 08 00 00 is the single-precision representation of the value 2.125, and as you might guess, 00 00 00 00 is the single-precision representation of 0. I believe they come out in reverse order due to the endian-ness of the machine, and on a big-endian machine I think you'd get 2.125 0 instead.

In C++ this would be something like a reinterpret_cast. In Java, there doesn't appear to be as direct a mapping, but the answers to this Stack Overflow question discuss some alternatives such as Serialization.

From running help typecast it looks like it changes the datatype, but keeps the bit assignment the same, whereas single( ) keeps the number the same, but changes the bit arrangement.

If I understand it, you could think of it like you have two boxes, each containing up to 8 balls. Lets say, box 1 is full, whilst box 2 contains 3 balls. We now typecast this into a system where a box holds 4 balls.

This system will need three boxes to hold our balls. So we have boxes 1 and 2 which are full. Box 3 contains 3 balls.

So you'd have [8,3] converted to [4,4,3].

Alternatively, if you converted the number into our new system in the same way as single( ) works (e.g. for changing an int8 to a single), you'd change the number of balls, not the container.