Unfamiliar .D0 number syntax

Question

Chad Greene 2022-3-7

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https://ww2.mathworks.cn/matlabcentral/answers/1665694-unfamiliar-d0-number-syntax

评论： James Tursa 2022-3-9

I've inherited some Matlab code that was previously adapted from Fortran, and the Matlab code has a syntax I'm not familiar with. Numbers end with .D0, so I see a lot of lines like:

a = b*5.D0;

which produces the same result as

a = b*5;

I haven't found any documentation for this syntax, but it's easy to deduce what it's doing:

>> 12345.D0
ans =
12345
>> 12345.D2
ans =
1234500
>> 12345.D-3
ans =
12.3450

My questions are:

What is this syntax called?
Is there any particular reason to use it?
Can I safely delete every instance of .D0 from this code I've inherited?

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Answer 1

Steven Lord 2022-3-7

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在 MATLAB Online 中打开

This is E notation. I believe MATLAB supports D as well as E because Cleve was inspired by Fortran, which as a comment on that page states "FORTRAN (at least since FORTRAN IV as of 1961) also uses "D" to signify double precision numbers in scientific notation."

x = 3.4e2
x = 340
y = 3.4d2
y = 340

The .D0 indicates that whatever value you're defining is an integer. All of z, w, and q are the same value (five.)

z = 5.0D0
z = 5
w = 5.D0
w = 5
q = 5D0
q = 5

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Chad Greene 2022-3-7

@Steven Lord Thanks, so I guess I can delete the .D0 instances from the code I inherited.

James Tursa 2022-3-9

@Chad Greene FYI, there is a difference between MATLAB and Fortran for the E notation. In MATLAB the E notation is a double variable same as D notation, but in Fortran the E notation is single precision, not double precision.

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