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Created
Sun, Oct 13, 10:31
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Tue, Oct 15, 10:31 (1 d, 22 h)
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Attached To
rSCINTROPAR Introduction to parallelism
pi.cc
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/*
This exercise is taken from the class Parallel Programming Workshop (MPI,
OpenMP and Advanced Topics) at HLRS given by Rolf Rabenseifner
*/
#include <chrono>
#include <cstdio>
#include <cmath>
#ifdef _OPENMP
#include <omp.h>
#endif
using
clk
=
std
::
chrono
::
high_resolution_clock
;
using
second
=
std
::
chrono
::
duration
<
double
>
;
using
time_point
=
std
::
chrono
::
time_point
<
clk
>
;
inline
int
digit
(
double
x
,
int
n
)
{
return
std
::
trunc
(
x
*
std
::
pow
(
10.
,
n
))
-
std
::
trunc
(
x
*
std
::
pow
(
10.
,
n
-
1
))
*
10.
;
}
inline
double
f
(
double
a
)
{
return
(
4.
/
(
1.
+
a
*
a
));
}
const
int
n
=
10000000
;
int
main
(
int
/* argc */
,
char
**
/* argv */
)
{
int
i
;
double
dx
,
x
,
sum
,
pi
;
int
nthreads
;
#ifdef _OPENMP
auto
omp_t1
=
omp_get_wtime
();
#endif
auto
t1
=
clk
::
now
();
/* calculate pi = integral [0..1] 4 / (1 + x**2) dx */
dx
=
1.
/
n
;
sum
=
0.0
;
for
(
i
=
1
;
i
<=
n
;
i
++
)
{
x
=
(
1.
*
i
-
0.5
)
*
dx
;
sum
=
sum
+
f
(
x
);
}
pi
=
dx
*
sum
;
#ifdef _OPENMP
auto
omp_elapsed
=
omp_get_wtime
()
-
omp_t1
;
#endif
second
elapsed
=
clk
::
now
()
-
t1
;
std
::
printf
(
"computed pi = %.16g
\n
"
,
pi
);
#ifdef _OPENMP
std
::
printf
(
"wall clock time (omp_get_wtime) = %.4gs in %d threads
\n
"
,
omp_elapsed
,
nthreads
);
#endif
std
::
printf
(
"wall clock time (chrono) = %.4gs
\n
"
,
elapsed
.
count
());
for
(
int
d
=
1
;
d
<=
15
;
++
d
)
{
std
::
printf
(
"%d"
,
digit
(
pi
,
d
));
}
return
0
;
}
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