error message unclear for initStateFromAmps

[nataliejpg]

When the number of amplitudes in the lists submitted to the initialisation function initStateFromAmps becomes too long (>24 qubits for QuEST_PREC=2 or >25 for QuEST_PREC=1) the programme crashes with the error message "segmentation fault". It would be helpful to have a warning in the documentation for this or generate an error message when the number of amplitudes exceeds the supported number.

[rrmeister]

Hi Natalie!
I cannot reproduce this on the current version of QuEST. Building the following with QuEST_PREC=2

#include <stdio.h>
#include <stdlib.h>
#include "QuEST.h"

int main (int narg, char *varg[]) {
    QuESTEnv env = createQuESTEnv();
    int numQb = 25;
    printf("allocating memory...\n");
    Qureg qubits = createQureg(numQb, env);
    long long int numAmps = 1ll << numQb;
    qreal* re_amps = malloc(numAmps * sizeof(qreal));
    qreal* im_amps = malloc(numAmps * sizeof(qreal));
    if (re_amps == NULL || im_amps == NULL) {
            printf("out of memory\n");
            return 1;
    }
    printf("allocated memory, randomly generating amplitudes...\n");
    for (long long int i = 0; i < numAmps; i++) {
            re_amps[i] = rand();
            im_amps[i] = rand();
    }
    printf("setting amplitudes...\n");
    initStateFromAmps(qubits, re_amps, im_amps);
    printf("successfully set amplitudes\n");
    free(re_amps);
    free(im_amps);
    destroyQureg(qubits, env);
    destroyQuESTEnv(env);
    return 0;
}

gives me the output

allocating memory...
allocated memory, randomly generating amplitudes...
setting amplitudes...
successfully set amplitudes

Can you post a minimal example to reproduce your issue?