Shakes Me Up: Numerical

Showing posts with label Numerical. Show all posts

Thursday, July 18, 2013

Fortran Garbage Collector

http://stackoverflow.com/questions/13966955/does-fortran-have-a-garbage-collectorgc/13967374#13967374

Modern Fortran has many ways of declaring variables. Items simply declared will exist for the duration of the scope of the entity. So "real, dimension (N) :: array" declared in a procedure will automatically disappear when that procedure returns. Naturally variables declared in the main program or module variables or common (outmoded) will persist for the duration of the program.

allocate -- dynamic allocate

Variables can be dynamically allocated with "allocate" (to do so, they have to be declared with the allocatable attribute). Since Fortran 95 allocatable variables that are local to a procedure are automatically deallocated when the procedure returns! They will not leak memory! (Some programmers might consider it good practice to explicitly deallocate the variables anyway, even though it isn't strictly necessary.) (Of course, you can waste memory in the sense of not explicitly deallocating a variable that you know that you don't need anymore.)

t is possible to leak memory with pointers. You can allocate memory with a pointer, then assign the pointer to to another variable, losing the previous association. If you didn't deallocate that memory you have a leak. The need for pointers is less in Fortran than in some other languages ... many things can be done with allocatable variables, which are safer -- no memory leaks

http://stackoverflow.com/questions/2300199/allocatable-arrays-or-pointer-arrays
Allocatable arrays Vs Pointer arrays?

Allocatable arrays can result in more efficient code because the arrays will be contiguous. Particularly if the array is passed to a subroutine, being contiguous can prevent the need for the compiler creating a temporary copy. For local variables in subroutines (without the SAVE attribute) (for Fortran 95 and higher), allocatable arrays are automatically deallocated upon exit from the subroutine, avoiding a memory leak. Memory leaks aren't possible with allocatables, except in the sense of the programmer not deallocating an array that is no longer need. With pointers, you can reassign a pointer, leaving some memory inaccessible and lost -- one form of a leak. If an allocatable will do the job, I recommend using that method instead of a pointer. Some reasons to use pointers: taking a section of an array, or creating a data structure such as a linked list. For the purpose of creating an array of size determined at run time, I'd use an allocatable.

Friday, July 12, 2013

HDF5 and Ubuntu

http://micro.stanford.edu/wiki/Install_HDF5#Ubuntu

Thursday, June 6, 2013

Pade Series

Padé approximant is the "best" approximation of a function by a rational function of given order – under this technique,

The Padé approximant often gives better approximation of the function than truncating its Taylor series, and it may still work where the Taylor series does not converge.

http://en.wikipedia.org/wiki/Pad%C3%A9_approximant