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/* grover.c: Implementation of Grover's search algorithm
Copyright 2003 Bjoern Butscher, Hendrik Weimer
This file is part of libquantum
libquantum is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published
by the Free Software Foundation; either version 3 of the License,
or (at your option) any later version.
libquantum is distributed in the hope that it will be useful, but
WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
General Public License for more details.
You should have received a copy of the GNU General Public License
along with libquantum; if not, write to the Free Software
Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston,
MA 02110-1301, USA
*/
#include <quantum.h>
#include <stdio.h>
#include <math.h>
#include <stdlib.h>
#include <time.h>
#ifdef M_PI
#define pi M_PI
#else
#define pi 3.141592654
#endif
void oracle(int state, quantum_reg *reg)
{
int i;
for(i=0;i<reg->width;i++)
{
if(!(state & (1 << i)))
{
quantum_sigma_x(i, reg);
}
}
quantum_toffoli(0, 1, reg->width+1, reg);
for(i=1;i<reg->width;i++)
{
quantum_toffoli(i, reg->width+i, reg->width+i+1, reg);
}
quantum_cnot(reg->width+i, reg->width, reg);
for(i=reg->width-1;i>0;i--)
{
quantum_toffoli(i, reg->width+i, reg->width+i+1, reg);
}
quantum_toffoli(0, 1, reg->width+1, reg);
for(i=0;i<reg->width;i++)
{
if(!(state & (1 << i)))
quantum_sigma_x(i, reg);
}
}
void inversion(quantum_reg *reg)
{
int i;
for(i=0;i<reg->width;i++)
quantum_sigma_x(i, reg);
quantum_hadamard(reg->width-1, reg);
if(reg->width==3)
quantum_toffoli(0, 1, 2, reg);
else
{
quantum_toffoli(0, 1, reg->width+1, reg);
for(i=1;i<reg->width-1;i++)
{
quantum_toffoli(i, reg->width+i, reg->width+i+1, reg);
}
quantum_cnot(reg->width+i, reg->width-1, reg);
for(i=reg->width-2;i>0;i--)
{
quantum_toffoli(i, reg->width+i, reg->width+i+1, reg);
}
quantum_toffoli(0, 1, reg->width+1, reg);
}
quantum_hadamard(reg->width-1, reg);
for(i=0;i<reg->width;i++)
quantum_sigma_x(i, reg);
}
void grover(int target, quantum_reg *reg)
{
int i;
oracle(target, reg);
for(i=0;i<reg->width;i++)
quantum_hadamard(i, reg);
inversion(reg);
for(i=0;i<reg->width;i++)
quantum_hadamard(i, reg);
}
int main(int argc, char **argv)
{
quantum_reg reg;
int i, N, width=0;
srand(time(0));
if(argc==1)
{
printf("Usage: grover [number] [[qubits]]\n\n");
return 3;
}
N=atoi(argv[1]);
if(argc > 2)
width = atoi(argv[2]);
if(width < quantum_getwidth(N+1))
width = quantum_getwidth(N+1);
reg = quantum_new_qureg(0, width);
// reg.width--;
quantum_sigma_x(reg.width, ®);
for(i=0;i<reg.width;i++)
quantum_hadamard(i, ®);
quantum_hadamard(reg.width, ®);
printf("Iterating %i times\n", (int) (pi/4*sqrt(1<<reg.width)));
for(i=1; i<=pi/4*sqrt(1 << reg.width); i++)
{
printf("Iteration #%i\n", i);
grover(N, ®);
}
quantum_hadamard(reg.width, ®);
reg.width++;
quantum_bmeasure(reg.width-1, ®);
for(i=0; i<reg.size; i++)
{
if(reg.state[i] == N)
printf("\nFound %i with a probability of %f\n\n", N,
quantum_prob(reg.amplitude[i]));
}
quantum_delete_qureg(®);
return 0;
}
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