Unfamiliar .D0 number syntax

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Chad Greene
Chad Greene on 7 Mar 2022
Commented: James Tursa on 9 Mar 2022
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:
  1. What is this syntax called?
  2. Is there any particular reason to use it?
  3. Can I safely delete every instance of .D0 from this code I've inherited?

Accepted Answer

Steven Lord
Steven Lord on 7 Mar 2022
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
  2 Comments
James Tursa
James Tursa on 9 Mar 2022
@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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