double u_dx1(void)
{
    int II0 = II;
    if(++II >= KK)  II = 0;     /*wrap around running index */
    XX[II] = DMOD(BB1 * XX[II] + XX[II0],  PP);
    return ((double) XX[II] /PP) + HH;
}
double u_dx2(void)
{
    int II0 = II;
    if(++II >= KK)  II = 0;     /*wrap around running index */
    XX[II] = DMOD(BB2 * (XX[II] + XX[II0]),  PP);
    return ((double) XX[II] /PP) + HH;
}
double u_dx3(void)
{
    int II0 = II;
    if(++II >= KK)  II = 0;     /*wrap around running index */
    if(++K12 >= KK) K12 = 0;    /*wrap around K12*/
    XX[II] = DMOD(BB3 * (XX[II] + XX[K12] + XX[II0]), PP);
    return ((double) XX[II] /PP) + HH;
}
double u_dx4(void)
{
    int II0 = II;
    if(++II >= KK)   II = 0;    /*wrap around running index */
    if(++K13 >= KK) K13 = 0;    /*wrap around K13*/
    if(++K23 >= KK) K23 = 0;    /*wrap around K23*/
    XX[II] = DMOD(BB4 * (XX[II]+XX[K13]+XX[K23]+XX[II0]), PP);
    return ((double) XX[II] /PP) + HH;
}