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41 #include "gmx_fatal.h"
45 #define CONVERGEITER 0.000000001
46 #define CLOSE_ENOUGH 0.000001000
48 #define CONVERGEITER 0.0001
49 #define CLOSE_ENOUGH 0.0050
52 /* we want to keep track of the close calls. If there are too many, there might be some other issues.
53 so we make sure that it's either less than some predetermined number, or if more than that number,
54 only some small fraction of the total. */
55 #define MAX_NUMBER_CLOSE 50
56 #define FRACTION_CLOSE 0.001
58 /* maximum length of cyclic traps to check, emerging from limited numerical precision */
61 void gmx_iterate_init(gmx_iterate_t *iterate,gmx_bool bIterate)
66 iterate->bIterate = bIterate;
67 iterate->num_close = 0;
68 for (i=0;i<MAXITERCONST+2;i++)
70 iterate->allrelerr[i] = 0;
74 gmx_bool done_iterating(const t_commrec *cr,FILE *fplog, int nsteps, gmx_iterate_t *iterate, gmx_bool bFirstIterate, real fom, real *newf)
76 /* monitor convergence, and use a secant search to propose new
79 The secant method computes x_{i+1} = x_{i} - f(x_{i}) * ---------------------
82 The function we are trying to zero is fom-x, where fom is the
83 "figure of merit" which is the pressure (or the veta value) we
84 would get by putting in an old value of the pressure or veta into
85 the incrementor function for the step or half step. I have
86 verified that this gives the same answer as self consistent
87 iteration, usually in many fewer steps, especially for small tau_p.
89 We could possibly eliminate an iteration with proper use
90 of the value from the previous step, but that would take a bit
91 more bookkeeping, especially for veta, since tests indicate the
92 function of veta on the last step is not sufficiently close to
93 guarantee convergence this step. This is
94 good enough for now. On my tests, I could use tau_p down to
95 0.02, which is smaller that would ever be necessary in
96 practice. Generally, 3-5 iterations will be sufficient */
106 iterate->f = fom-iterate->x;
113 iterate->f = fom-iterate->x; /* we want to zero this difference */
114 if ((iterate->iter_i > 1) && (iterate->iter_i < MAXITERCONST))
116 if (iterate->f==iterate->fprev)
122 *newf = iterate->x - (iterate->x-iterate->xprev)*(iterate->f)/(iterate->f-iterate->fprev);
127 /* just use self-consistent iteration the first step to initialize, or
128 if it's not converging (which happens occasionally -- need to investigate why) */
132 /* Consider a slight shortcut allowing us to exit one sooner -- we check the
133 difference between the closest of x and xprev to the new
134 value. To be 100% certain, we should check the difference between
135 the last result, and the previous result, or
137 relerr = (fabs((x-xprev)/fom));
139 but this is pretty much never necessary under typical conditions.
140 Checking numerically, it seems to lead to almost exactly the same
141 trajectories, but there are small differences out a few decimal
142 places in the pressure, and eventually in the v_eta, but it could
145 if (fabs(*newf-x) < fabs(*newf - xprev)) { xmin = x;} else { xmin = xprev;}
146 relerr = (fabs((*newf-xmin) / *newf));
149 err = fabs((iterate->f-iterate->fprev));
150 relerr = fabs(err/fom);
152 iterate->allrelerr[iterate->iter_i] = relerr;
154 if (iterate->iter_i > 0)
158 fprintf(debug,"Iterating NPT constraints: %6i %20.12f%14.6g%20.12f\n",
159 iterate->iter_i,fom,relerr,*newf);
162 if ((relerr < CONVERGEITER) || (err < CONVERGEITER) || (fom==0) || ((iterate->x == iterate->xprev) && iterate->iter_i > 1))
164 iterate->bIterate = FALSE;
167 fprintf(debug,"Iterating NPT constraints: CONVERGED\n");
171 if (iterate->iter_i > MAXITERCONST)
173 if (relerr < CLOSE_ENOUGH)
176 for (i=1;i<CYCLEMAX;i++) {
177 if ((iterate->allrelerr[iterate->iter_i-(1+i)] == iterate->allrelerr[iterate->iter_i-1]) &&
178 (iterate->allrelerr[iterate->iter_i-(1+i)] == iterate->allrelerr[iterate->iter_i-(1+2*i)])) {
182 fprintf(debug,"Exiting from an NPT iterating cycle of length %d\n",i);
189 /* step 1: trapped in a numerical attractor */
190 /* we are trapped in a numerical attractor, and can't converge any more, and are close to the final result.
191 Better to give up convergence here than have the simulation die.
193 iterate->num_close++;
198 /* Step #2: test if we are reasonably close for other reasons, then monitor the number. If not, die */
200 /* how many close calls have we had? If less than a few, we're OK */
201 if (iterate->num_close < MAX_NUMBER_CLOSE)
203 sprintf(buf,"Slight numerical convergence deviation with NPT at step %d, relative error only %10.5g, likely not a problem, continuing\n",nsteps,relerr);
204 md_print_warning(cr,fplog,buf);
205 iterate->num_close++;
207 /* if more than a few, check the total fraction. If too high, die. */
208 } else if (iterate->num_close/(double)nsteps > FRACTION_CLOSE) {
209 gmx_fatal(FARGS,"Could not converge NPT constraints, too many exceptions (%d%%\n",iterate->num_close/(double)nsteps);
215 gmx_fatal(FARGS,"Could not converge NPT constraints\n");
220 iterate->xprev = iterate->x;
222 iterate->fprev = iterate->f;