Hi guys.could you help me please?

actually, i have three number, I want to compare the first digit of each number to the other

for example A=803.555 B=803.654 C=522.533 I have to compare 8,8 and 5 ..here they are not equal, therefore I have to do some things on the other hand A=803.555 B=803.654 C=803.544 I have to compare 8,8 and 5..here they are equal. so I have to do some things else

in general, how to write a commend to compare them thank you

[Torsten]

What about A=803.555, B=803.654 and C=4834.456 ? Are the "first digits" 8,8,8 or 8,8,4 ?

Best wishes

Torsten.

[Hussein Ali]

8,8,4

[Birdman]

Check my answer.

[Steven Lord]

Assuming you're able to extract that information, what are you planning to do with it? There may be a way to achieve your goal without trying to decompose the numbers into their individual digits.

Answer 1

[Birdman]

Firstly, convert them to string.

A=num2str(A);
B=num2str(B);
C=num2str(C);

Then, compare their first digit by writing

str2double(A(1))>str2double(B(1))

or

A(1)>B(1)

Same applies for all combinations. Note that it is not relevant to convert them to numeric again.

[Walter Roberson]

You do not need to convert them to numeric again to compare them. The characters are in the order '0' '1' '2' '3' '4' '5' '6' '7' '8' '9', so for example '8' > '5'

[Birdman]

That is also a way, thanks.

[Hussein Ali]

Is it valid for the values come form prevouse calculation like

     if MAX==2
            A=(pdummy(iter-1,1))
            A=num2str(A)
            B=(pdummy(iter-1,2))
            B=num2str(B)
            C=(pdummy(iter-1,3))
            C=num2str(3)
            if str2double(A(1))> str2double(B(1)) ||str2double(C(1))> str2double(C(1))
               pdummy(iter-1,:)=sort(pdummy(iter-1,:),'descend')
               Dref=Dref-dStep     
            end

[Birdman]

What is the value for iter? What is pdummy?

If you store your previous values in an array, then it should be possible.

[Hussein Ali]

in image enclosed please, look to last iteration (803.4256 803.4255 522.6808) the third value is different.

what I want to do is comparing the values of the last iteration to do some things if they are not equal if they are equal. it is okey

[Hussein Ali]

when i used what you told I had to get the following message:- The function 'num2str' is not supported for standalone code generation. See the documentation for coder.extrinsic to learn how you can use this function in simulation

[Jan]

You could use sprintf instead of the slower num2str, but the conversion to a string is indirect and I expect it to be slower than staying at the original numerical type.

[Birdman]

The function 'num2str' is not supported for standalone code generation. See the documentation for coder.extrinsic to learn how you can use this function in simulation

Code generation is completely a different stuff. Simulink only works with numeric variables, therefore my approach will fail there. You need to consider another way.

[EDITED]:

Here is an implementation of Jan's function in Simulink: Check the attached model, run it and see the results.

[Walter Roberson]

Note that sprintf() is not supported by MATLAB Coder.

Answer 2

[Jan]

The conversion to a char vector by sprintf or num2str is short an easy sometimes, but internally a lot of computations are required for these functions. It might be more efficient to stay at the original data type and get the value of the first digit by using log10:

A = 803.555
B = 803.654
C = 522.533
A1 = getFirstDigit(A);
B1 = getFirstDigit(B);
C1 = getFirstDigit(C);
if isequal(A1, B1, C1)
  ...
else
  ...
end

function D = getFirstDigit(X)
D = floor(X ./ 10 .^ floor(log10(X)));
end

You can call this with an array also:

Digits = getFirstDigit([A, B, C])

[Stephen23]

+1 nice concept.

[Jan]

@Stephen: Thanks. The analysis of the input using log10 must happen internally in sprintf also, and in consequence in num2str. But getFirstDigit avoids to parse the rest of the number in addition.