I can't figure out what in the world this "9999" is doing in front of the e20.8, in the label of this fortran write statement.
Is does not refer to any other line in the code. In other words, there isn't a line labeled 9999 to which it refers, elsewhere in the program.
write(11,'(9999e20.8)') (9999.0, i=1,2*(numant+numunique))
I'm boggled - I haven't found the answer from google web searches, although I think I get the general picture about write statement syntax and formatting.
Is this enough info provided to make sense?
It's a repetition count; the general format for a format code is (count)(type)(format), eg as described in this tutorial here.
Unlike C-based languages, unused formatting codes are simply ignored, so this line essentially says "write out as many real numbers in scientific format (with 8 digits after the decimal) as there are in the following output list". (If you don't like doing it this way, with a hardcoded "big enough" number, you'd have to programatically generate the format string to have the "right" repetition code.
The output list is an implied-do loop, which generates the number 9999.0 2*(numant+numuniqe) times.
Related
I have little knowledge of the Fortran language. I have come across some programs written in the 90s (see attached snapshot showing just a portion of a long script).
I'd like to know what kind of compiler is appropriate to execute such codes? I have installed gfortran-4.2.3 on my mac. I'm also not sure about the indentation in the attached code: if C (comment) is at column 1, does the main code start at column 9 or 7? what about the position of numbers placed in between referred by GO TO?
This is not Fortran 90. This is Fortran 77.
That said, gfortran is able to compile this code. Make sure that the file extension for the file is .f so that gfortran realises it's fixed-form.
The C needs to be in the first column, the numbers that you reference are labels, they can be between column 1 and 5. The asterisk at line 198 is a continuation character, meaning that this should be treated as part of the previous line. It must be in column 6. Everything else needs to be between columns 7 and 72 (inclusive)
Oh, and the 3-digit numbers at the very beginning are line numbers, and must not be in the source code.
Edited to add: Since you have to type it all again anyway, you might as well make it free-form:
Replace the C in the first column with !, and change the way continuation lines are marked: Turn this:
write (*, *) "This is some long text,
* which doesn't fit into a line"
Into this:
write(*, *) "This is some long text, " // &
"which doesn't fit into a line"
Everything else can stay like it is. (You can now use proper indentation, too!)
New Edit
So you've pasted the code that you wrote and the error messages, so I'm replying to that now.
In Fixed Form, any character past column 72 is ignored. You have a few lines with long strings, where the terminating quotation mark is in that ignored region.
Make sure that no line exceeds the 72nd row.
Hy everybody, I've found some problems in reading unformatted character strings in a simple file. When the first / is found, everything is missed after it.
This is the example of the text I would like to read: after the first 18 character blocks that are fixed (from #Mod to Flow[kW]), there is a list of chemical species' names, that are variables (in this case 5) within the program I'm writing.
#Mod ID Mod Name Type C. #Coll MF[kg/s] Pres.[Pa] Pres.[bar] Temp.[K] Temp.[C] Ent[kJ/kg K] Power[kW] RPM[rad/s] Heat Flow[kW] METHANE ETHANE PROPANE NITROGEN H2O
I would like to skip, after some formal checks, the first 18 blocks, then read the chemical species. To do the former, I created a character array with dimension of 18, each with a length of 20.
character(20), dimension(18) :: chapp
Then I would like to associate the 18 blocks to the character array
read(1,*) (chapp(i),i=1,18)
...but this is the result: from chapp(1) to chapp(7) are saved the right first 7 strings, but this is chapp(8)
chapp(8) = 'MF[kg '
and from here on, everything is leaved blank!
How could I overcome this reading problem?
The problem is due to your using list-directed input (the * as the format). List-directed input is useful for quick and dirty input, but it has its limitations and quirks.
You stumbled across a quirk: A slash (/) in the input terminates assignment of values to the input list for the READ statement. This is exactly the behavior that you described above.
This is not choice of the compiler writer, but is mandated by all relevant Fortran standards.
The solution is to use formatted input. There are several options for this:
If you know that your labels will always be in the same columns, you can use a format string like '(1X,A4,2X,A2,1X,A3,2X)' (this is not complete) to read in the individual labels. This is error-prone, and is also bad if the program that writes out the data changes format for some reason or other, or if the labes are edited by hand.
If you can control the program that writes the label, you can use tab characters to separate the individual labels (and also, later, the labels). Read in the whole line, split it into tab-separated substrings using INDEX and read in the individual fields using an (A) format. Don't use list-directed format, or you will get hit by the / quirk mentioned above. This has the advantage that your labels can also include spaces, and that the data can be imported from/to Excel rather easily. This is what I usually do in such cases.
Otherwise, you can read in the whole line and split on multiple spaces. A bit more complicated than splitting on single tab characters, but it may be the best option if you cannot control the data source. You cannot have labels containing spaces then.
The program can run, I am not sure how to use open() and save the data in another external file name output.txt. My questions are stated below - please have a look and help.
program start
implicit none
integer ::n
real(kind=8)::x,h,k
real(kind=8),external:: taylorq
x=1.0
n=20
h=exp(x)
k=taylorq(x,n)
open(10,'output.txt') ----------- *question1:(when should i put this open file?)*
write(*,*)"The exact value=",h
write(*,*)"The approximate value=",k
write(*,*)"The error=",h-k
end program start
function taylorq(x,n)
implicit none
integer::n,i
real(kind=8):: x,taylor,taylor2,taylorq,h
h=exp(x)
taylor=1.
taylor2=taylor
write(*,*)"i exact appro error"-----------question2:(actually I want to draw a table with subtitle i, exact, appro, error in each column, is there a nice way to arrange them like eg.we can use %5s)
do i=1,n
taylor=taylor*x/i
taylor2=taylor2+taylor
write(10,*)i,h,taylor2,taylor2-h --------question3:*(I want to save the data written here into file output.txt)*
end do
close(10)
taylorq=taylor2
end function taylorq
1. where to open
You should put open(10,...) so it executes before any write(10,...) -- or read(10,...) if this was input.
Since your writes occur in the function taylorq, you should open() before the statement that calls taylorq.
For programs that do very large computations, which Fortran is suited/famous for, it is often best to do
all file open's very near the beginning of the program, so that if there is a problem opening any file,
it is caught and fixed without wasting hours or days of work. But your program is much simpler than that.
2. formatting
Yes, Fortran can do formatted output -- and also formatted input. Instead of a text string with
interpolated specifiers (like C and the C part of C++, and Java, and awk and perl and shell) it uses specifiers
with optionally interpolated text values, and the specifiers are written with the format letter on
the left followed by the width (almost always) and other parameters (sometimes).
You can either put the format directly in the WRITE (or READ) statement, or in a separate FORMAT
statement referred to by its label in the I/O statement.
write (10, '(I4,F10.2,F10.2,F10.2)' ) i,h,taylor2,taylor2-h
or
write (10, 900) i,h,taylor2,taylor2-h
! this next line can be anywhere in the same program-unit
900 format (I4,F10.2,F10.2,F10.2)
Unlike C-family languages, Fortran will always output the specified width; if the value doesn't fit,
it prints asterisks ***** instead of forcing the field wider (and thus misaligned) (or truncating as
COBOL does!). Your series grows fast enough you might want to use scientific notation like E10.3.
(The format letters can be in either case, but I find them easier to read in upper. YMMV.)
There are many, MANY, more options. Any textbook or your compiler manual should cover this.
I am new to regex and struggling to create an expression to parse a csv containing 1 to n values. The values can be integers or real numbers. The sample inputs would be:
1
1,2,3,4,5
1,2.456, 3.08, 0.5, 7
This would be used in c#.
Thanks,
Jerry
Use a CSV parser instead of RegEx.
There are several options - see this SO questions and answers and this one for the different options (built into the BCL and third party libraries).
The BCL provides the TextFieldParser (within the VisualBasic namespace, but don't let that put you off it).
A third party library that is liked by many is filehelpers.
Using REGEX for CSV parsing has been a 10 year jihad for me. I have found it remarkably frustrating, due to the boundary cases:
Numbers come in a variety of forms (here in the US, Canada):
1
1.
1.0
1000
1000.
1,000
1e3
1.0e3
1.0e+3
1.0e+003
-1
-1.0 (etc)
But of course, Europe has traditionally been different with regard to commas and decimal points:
1
1,0
1000
1.000e3
1e3
1,0e3
1,0e+3
1,0e+003
Which just ruins everything. So, we ignore the German and French and Continental standard because the comma just is impossible to work out whether it is separating values, or part of values. (The Continent likes TAB instead of COMMA)
I'll assume that you're "just" looking for numerical values separated from each other by commas and possible space-padding. The expression:
\s*(\-?\d+(?:\.\d*)?(?:[eE][\-+]?\d*)?)\s*
is a pretty fair parser of A NUMBER. Catches just about every reasonable case. Doesn't deal with imbedded commas though! It also trims off spaces, either side of the number.
From there, you can either build an iterative CSV string decomposer (walking each field, absorbing commas, assigning to an array, say), or use the scanf type function to do the same thing. I do prefer the iterative decomposition method - as it also allows you to parse out strings, hexadecimal, and virtually any other pattern you find in the data.
The regex you want is
#"([+-]?\d+(?:\.\d+)?)(?:$|,\s*)"
...from which you'll want capture group 1. However, don't use regex for something like this. String manipulation is much better when the input is in a very static, predictable format:
string[] nums = strInput.split(", ".ToCharArray(), StringSplitOptions.RemoveEmptyEntries);
List<float> results = (from n in nums
select float.Parse(n)).ToList();
If you do use regex, make sure you do a global capture.
I think you would have to loop it to check for an unknown number of ints... or else something like this:
/ *([0-9.]*) *,? *([0-9.]*) *,? *([0-9.]*) *,? *([0-9.]*) *,? *([0-9.]*) */
and you could keep that going ",?([0-9]*)" as far as you wanted to, to account for a lot of numbers. The result would be an array of numbers....
http://jsfiddle.net/8URvL/1/
I am writing some simple output in fortran, but I want whitespace delimiters. If use the following statement, however:
format(A20,ES18.8,A12,ES18.8)
I get output like this:
p001t0000 3.49141273E+01obsgp_oden 1.00000000E+00
I would prefer this:
p001t0000 3.49141273E+01 obsgp_oden 1.00000000E+00
I tried using negative values for width (like in Python) but no dice. So, is there a way to left-justify the numbers?
Many thanks in advance!
There's not a particularly beautiful way. However, using an internal WRITE statement to convert the number to a text string (formerly done with an ENCODE statement), and then manipulating the text may do what you need.
Quoting http://rsusu1.rnd.runnet.ru/develop/fortran/prof77/node168.html
An internal file WRITE is typically
used to convert a numerical value to a
character string by using a suitable
format specification, for example:
CHARACTER*8 CVAL
RVALUE = 98.6
WRITE(CVAL, '(SP, F7.2)') RVALUE
The WRITE statement will fill the
character variable CVAL with the
characters ' +98.60 ' (note that there
is one blank at each end of the
number, the first because the number
is right-justified in the field of 7
characters, the second because the
record is padded out to the declared
length of 8 characters).
Once a number has been turned into a
character-string it can be processed
further in the various ways described
in section 7. This makes it possible,
for example, to write numbers
left-justified in a field, ...
This is easier with Fortran 95, but still not trivial. Write the number or other item to a string with a write statement (as in the first answer). Then use the Fortran 95 intrinsic "ADJUSTL" to left adjust the non-blank characters of the string.
And really un-elegant is my method (I program like a cave woman), after writing the simple Fortran write format (which is not LJ), I use a combination of Excel (csv) and ultraedit to remove the spaces effectively getting the desired LJ followed directly by commas (which I need for my specific import format to another software). BF
If what you really want is whitespace between output fields rather than left-justified numbers to leave whitespace you could simply use the X edit descriptor. For example
format(A20,4X,ES18.8,4X,A12,4X,ES18.8)
will insert 4 spaces between each field and the next. Note that the standard requires 1X for one space, some of the current compilers accept the non-standard X too.
!for left-justified float with 1 decimal.. the number to the right of the decimal is how many decimals are required. Write rounds to the desired decimal space automatically, rather than truncating.
write(*, ['(f0.1)']) RValue !or
write(*, '(f0.1)') RValue
!for left-justified integers..
write(*, ['(i0)']) intValue !or
write(*, '(i0)') RValue
*after feedback from Vladimir, retesting proved the command works with or without the array brackets