MATLAB: Storing value in a variable

MATLABmatlab functionvariable

According to my knowledge, the in x we can store values from -127 to 127. then why on executing this code, x=250 and x=3*10^12 is getting stored inx?

int8 x

intmax("int8")

x=35

x=250

x=30000000000000000000

Best Answer

It looks like you are trying to declare a variable type. MATLAB does not have variable type declarations.

This is what your MATLAB code is actually doing:

int8 x                  % convert the character 'x' to int8.
intmax("int8")          % call INTMAX for "int8".
x=35                    % define a double with value 35, give it the variable name x
x=250                   % define a double with value 250, give it the variable name x
x=30000000000000000000  % define a double with value 3e20, give it the variable name x

None of these commands have anything to do with each other. None of them have any effect on each other.

The first two lines assign their outputs to the default ans. The behavior of the first line is explained here:

https://www.mathworks.com/help/matlab/matlab_prog/command-vs-function-syntax.html

Here are the two common ways in MATLAB of converting a value to a particular class, either specify the class:

>> x = int8(250)
x = 127

or using indexing to assign to an existing array of that class:

>> x = zeros(1,1,'int8');
>> x(1) = 250
x = 127

Related Solutions

MATLAB: It is necessary to declare the data type each time I change the value

MATLAB does not give you the ability to set a variable name as automatically a specific data type. (Unlike old Fortran, where I could tell it that all variables that begin with the letters i through n were of integer type automatically.)

So even though you initially assign

x = int8(9);

then when you do this:

x = 2;

MATLAB sees that 2 is a double precision value, and the assignment "x=" overrides the current datatype of x. So x is now a double.

You have two choices that I can think of.

x = int8(2);

must work of course, since that just overwrites x. But you can also use this form:

x(:) = 2;

x was initially a scalar, of class int8. But the assignment as x(:)= does not overwrite the variable type. It uses the current type of x. As a test try this:

x = int8(9);
whos x
Name      Size            Bytes  Class    Attributes
x         1x1                 1  int8               
x(:) = 2;
whos x
Name      Size            Bytes  Class    Attributes
x         1x1                 1  int8               
x
x =
  int8
   2

So x remains an int8, without needing to recast x as int8.

MATLAB: Write a function called integerize that takes as its input a matrix A of integers of type double, and returns the name of the “smallest” signed integer class to which A can be converted without loss of information.

A simpler implementation:

function text = integerize(A)
if A >= intmin('int8') & A <= intmax('int8')
    typ = 'int8';
elseif A >= intmin('int16') & A <= intmax('int16')
    typ = 'int16';
elseif A >= intmin('int32') & A <= intmax('int32')
    typ = 'int32';
elseif A >= intmin('int64') & A <= intmax('int64')
    typ = 'int64';
else
    typ = 'NONE';
end
end

And tested:

>> A = [128,127;-127,0];
>> integerize(A)
ans = int16

int16 is correct because 128 cannot be encoded by int8, but can be by int16 or larger:

>> intmax('int8')
ans = 127

Best Answer

Related Solutions

MATLAB: It is necessary to declare the data type each time I change the value

MATLAB: Write a function called integerize that takes as its input a matrix A of integers of type double, and returns the name of the “smallest” signed integer class to which A can be converted without loss of information.

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