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. If no such class exists, the text '

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abdelrahman mohamed 2018-10-29

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评论： abdelrahman mohamed 2018-11-1

%for every input the function gives int8 as an output
function x=integerize(A)
[m,n]=size(A);
for ii=1:m
    for jj=1:n
 if isa(A(ii,jj),'double')
     b=min(A); 
   if -128 <= b <= ((2^7)-1)
           x='int8';
       elseif (-2^15)<= b <= ((2^15)-1)
           x='int16';
       elseif (-2^31)<=b<= ((-2^31)-1)
           x='int32';
       elseif (-2^63)<=b<=((2^63)-1)
           x='int64';
       else
           x='NONE';
   end
   else
       x='NONE';
   end
      end
  end

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Walter Roberson 2018-10-29

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Answer 1

James Tursa 2018-10-29

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编辑：James Tursa 2018-10-29

在 MATLAB Online 中打开

You can't write multiple if conditions this way in MATLAB:

if -128 <= b <= ((2^7)-1)

You have to break it up into individual conditions. E.g.,

if -128 <= b & b <= ((2^7)-1)

Why are you doing the following:

b=min(A);

Hint: The following will turn A into a column vector of all the elements:

b = A(:);

Instead of using for loops, you can then write logic to test all of the elements of b at once to get your result.

Caution: You are going to have a problem with this part of your test for int64:

elseif (-2^63)<=b & b<=((2^63)-1)

The reason is that an int64 actually has more precision than a double, so you can get into trouble comparing numbers near the limits. E.g.,

>> intmax('int64')
ans =
  int64
   9223372036854775807
>> b = 2^63;
>> num2strexact(b)
ans =
    '9.223372036854775808e18'

Just looking at these numbers you can see that b is too large to fit in an int64 class variable. But look what happens with the test that you have:

>> b <= ((2^63)-1)
ans =
  logical
   1

It returned true! Obviously this is an incorrect result for what you are trying to test. What is the problem? It is the fact that a double precision variable does not have enough precision to do the (2^63)-1 calculation exactly. E.g.,

>> eps(2^63)
ans =
        2048

The spacing between numbers near 2^63 in IEEE double is 2048, much larger than the 1 you are trying to do arithmetic with. E.g., look at these results:

>> num2strexact((2^63))
ans =
    '9.223372036854775808e18'
>> num2strexact((2^63)-1)
ans =
    '9.223372036854775808e18'
>> num2strexact((2^63)-10)
ans =
    '9.223372036854775808e18'
>> num2strexact((2^63)-100)
ans =
    '9.223372036854775808e18'

You get the same number in each case. Subtracting 1, 10, or 100 had no effect on the answer because they are too far below eps(2^63). So, you will need to rewrite this test. Hint: What would happen if you tried to do this test in int64 arithmetic instead of double arithmetic? Try it out ...

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abdelrahman mohamed 2018-11-1

在 MATLAB Online 中打开

function x=integerize(A)

     b= min(A(:));
 % i have an error with A=[128 127,-127 0]
if (b>= -128) && (b <= ((128)-1))
       x='int8';
   elseif (-2^15)<= b && b <= ((2^15)-1)
       x='int16';
   elseif (-2^31)<=b && b<= ((-2^31)-1)
       x='int32';
   elseif intmin('int64')<= b && b<=intmax('int64')
       x='int64';
   else
       x='NONE';
   end