{

double a;

double b;

double error;

double exact;

int i;

int id;

double my_a;

double my_b;

int my_n;

double my_total;

int n;

int p;

int q;

int source;

MPI::Status status;

int tag;

int target;

double total;

double wtime;

double x;

a = 0.0;

b = 10.0;

n = 1000000000;

exact = 0.49936338107645674464;

MPI::Init ( argc, argv );

id = MPI::COMM_WORLD.Get_rank ( );

p = MPI::COMM_WORLD.Get_size ( );

if ( id == 0 )

{

my_n = n / ( p - 1 );

n = ( p - 1 ) * my_n;

wtime = MPI::Wtime ( );

timestamp ( );

cout << "\n";

cout << "QUAD_MPI\n";

cout << " C++/MPI version\n";

cout << " Estimate an integral of f(x) from A to B.\n";

cout << " f(x) = 50 / (pi * ( 2500 * x * x + 1 ) )\n";

cout << "\n";

cout << " A = " << a << "\n";

cout << " B = " << b << "\n";

cout << " N = " << n << "\n";

cout << " EXACT = " << setw(24) << setprecision(16) << exact << "\n";

cout << "\n";

cout << " Use MPI to divide the computation among " << p << " total processes,\n";

cout << " of which one is the master and does not do core computations.\n";

}

source = 0;

MPI::COMM_WORLD.Bcast ( &my_n, 1, MPI::INT, source );

if ( id == 0 )

{

for ( q = 1; q <= p - 1; q++ )

{

my_a = ( ( double ) ( p - q ) * a

+ ( double ) ( q - 1 ) * b )

/ ( double ) ( p - 1 );

target = q;

tag = 1;

MPI::COMM_WORLD.Send ( &my_a, 1, MPI::DOUBLE, target, tag );

my_b = ( ( double ) ( p - q - 1 ) * a

+ ( double ) ( q ) * b )

/ ( double ) ( p - 1 );

target = q;

tag = 2;

MPI::COMM_WORLD.Send ( &my_b, 1, MPI::DOUBLE, target, tag );

}

total = 0.0;

my_total = 0.0;

}

else

{

source = 0;

tag = 1;

MPI::COMM_WORLD.Recv ( &my_a, 1, MPI::DOUBLE, source, tag, status );

source = 0;

tag = 2;

MPI::COMM_WORLD.Recv ( &my_b, 1, MPI::DOUBLE, source, tag, status );

my_total = 0.0;

for ( i = 1; i <= my_n; i++ )

{

x = ( ( double ) ( my_n - i ) * my_a

+ ( double ) ( i - 1 ) * my_b )

/ ( double ) ( my_n - 1 );

my_total = my_total + f ( x );

}

my_total = ( my_b - my_a ) * my_total / ( double ) ( my_n );

cout << " Process " << id << " contributed MY_TOTAL = "

<< my_total << "\n";

}

MPI::COMM_WORLD.Reduce ( &my_total, &total, 1, MPI::DOUBLE, MPI::SUM, 0 );

if ( id == 0 )

{

error = fabs ( total - exact );

wtime = MPI::Wtime ( ) - wtime;

cout << "\n";

cout << " Estimate = " << setw(24) << setprecision(16) << total << "\n";

cout << " Error = " << error << "\n";

cout << " Time = " << wtime << "\n";

}

MPI::Finalize ( );

if ( id == 0 )

{

cout << "\n";

cout << "QUAD_MPI:\n";

cout << " Normal end of execution.\n";

cout << "\n";

timestamp ( );

}

return 0;

{

double pi;

double value;

pi = 3.141592653589793;

value = 50.0 / ( pi * ( 2500.0 * x * x + 1.0 ) );

return value;

{

# define TIME_SIZE 40

static char time_buffer[TIME_SIZE];

const struct std::tm *tm_ptr;

size_t len;

std::time_t now;

now = std::time ( NULL );

tm_ptr = std::localtime ( &now );

len = std::strftime ( time_buffer, TIME_SIZE, "%d %B %Y %I:%M:%S %p", tm_ptr );

std::cout << time_buffer << "\n";

return;

# undef TIME_SIZE