2: /* fnoise/snesdnest.F -- translated by f2c (version 20020314).
3: */
4: #include <petscsys.h>
5: #define FALSE_ 0 6: #define TRUE_ 1 8: /* Noise estimation routine, written by Jorge More'. Details are below. */
10: /* Subroutine */ PetscErrorCode SNESNoise_dnest_(PetscInt *nf, double *fval,double *h__,double *fnoise, double *fder2, double *hopt, PetscInt *info, double *eps)
11: {
12: /* Initialized data */
14: static double const__[15] = { .71,.41,.23,.12,.063,.033,.018,.0089,
15: .0046,.0024,.0012,6.1e-4,3.1e-4,1.6e-4,8e-5 };
17: /* System generated locals */
18: PetscInt i__1;
19: double d__1, d__2, d__3, d__4;
22: /* Local variables */
23: static double emin, emax;
24: static PetscInt dsgn[6];
25: static double f_max, f_min, stdv;
26: static PetscInt i__, j;
27: static double scale;
28: static PetscInt mh;
29: static PetscInt cancel[6], dnoise;
30: static double err2, est1, est2, est3, est4;
32: /* ********** */
34: /* Subroutine dnest */
36: /* This subroutine estimates the noise in a function */
37: /* and provides estimates of the optimal difference parameter */
38: /* for a forward-difference approximation. */
40: /* The user must provide a difference parameter h, and the */
41: /* function value at nf points centered around the current point. */
42: /* For example, if nf = 7, the user must provide */
44: /* f(x-2*h), f(x-h), f(x), f(x+h), f(x+2*h), */
46: /* in the array fval. The use of nf = 7 function evaluations is */
47: /* recommended. */
49: /* The noise in the function is roughly defined as the variance in */
50: /* the computed value of the function. The noise in the function */
51: /* provides valuable information. For example, function values */
52: /* smaller than the noise should be considered to be zero. */
54: /* This subroutine requires an initial estimate for h. Under estimates */
55: /* are usually preferred. If noise is not detected, the user should */
56: /* increase or decrease h according to the ouput value of info. */
57: /* In most cases, the subroutine detects noise with the initial */
58: /* value of h. */
60: /* The subroutine statement is */
62: /* subroutine dnest(nf,fval,h,hopt,fnoise,info,eps) */
64: /* where */
66: /* nf is an int variable. */
67: /* On entry nf is the number of function values. */
68: /* On exit nf is unchanged. */
70: /* f is a double precision array of dimension nf. */
71: /* On entry f contains the function values. */
72: /* On exit f is overwritten. */
74: /* h is a double precision variable. */
75: /* On entry h is an estimate of the optimal difference parameter. */
76: /* On exit h is unchanged. */
78: /* fnoise is a double precision variable. */
79: /* On entry fnoise need not be specified. */
80: /* On exit fnoise is set to an estimate of the function noise */
81: /* if noise is detected; otherwise fnoise is set to zero. */
83: /* hopt is a double precision variable. */
84: /* On entry hopt need not be specified. */
85: /* On exit hopt is set to an estimate of the optimal difference */
86: /* parameter if noise is detected; otherwise hopt is set to zero. */
88: /* info is an int variable. */
89: /* On entry info need not be specified. */
90: /* On exit info is set as follows: */
92: /* info = 1 Noise has been detected. */
94: /* info = 2 Noise has not been detected; h is too small. */
95: /* Try 100*h for the next value of h. */
97: /* info = 3 Noise has not been detected; h is too large. */
98: /* Try h/100 for the next value of h. */
100: /* info = 4 Noise has been detected but the estimate of hopt */
101: /* is not reliable; h is too small. */
103: /* eps is a double precision work array of dimension nf. */
105: /* MINPACK-2 Project. April 1997. */
106: /* Argonne National Laboratory. */
107: /* Jorge J. More'. */
109: /* ********** */
110: /* Parameter adjustments */
111: --eps;
112: --fval;
114: /* Function Body */
115: *fnoise = 0.;
116: *fder2 = 0.;
117: *hopt = 0.;
118: /* Compute an estimate of the second derivative and */
119: /* determine a bound on the error. */
120: mh = (*nf + 1) / 2;
121: est1 = (fval[mh + 1] - fval[mh] * 2 + fval[mh - 1]) / *h__ / *h__;
122: est2 = (fval[mh + 2] - fval[mh] * 2 + fval[mh - 2]) / (*h__ * 2) / (*h__ * 2);
123: est3 = (fval[mh + 3] - fval[mh] * 2 + fval[mh - 3]) / (*h__ * 3) / (*h__ * 3);
124: est4 = (est1 + est2 + est3) / 3;
125: /* Computing MAX */
126: /* Computing PETSCMAX */
127: d__3 = PetscMax(est1,est2);
128: /* Computing MIN */
129: d__4 = PetscMin(est1,est2);
130: d__1 = PetscMax(d__3,est3) - est4, d__2 = est4 - PetscMin(d__4,est3);
131: err2 = PetscMax(d__1,d__2);
132: /* write (2,123) est1, est2, est3 */
133: /* 123 format ('Second derivative estimates', 3d12.2) */
134: if (err2 <= PetscAbsScalar(est4) * .1) *fder2 = est4;
135: else if (err2 < PetscAbsScalar(est4)) *fder2 = est3;
136: else *fder2 = 0.;
138: /* Compute the range of function values. */
139: f_min = fval[1];
140: f_max = fval[1];
141: i__1 = *nf;
142: for (i__ = 2; i__ <= i__1; ++i__) {
143: /* Computing MIN */
144: d__1 = f_min, d__2 = fval[i__];
145: f_min = PetscMin(d__1,d__2);
147: /* Computing MAX */
148: d__1 = f_max, d__2 = fval[i__];
149: f_max = PetscMax(d__1,d__2);
150: }
151: /* Construct the difference table. */
152: dnoise = FALSE_;
153: for (j = 1; j <= 6; ++j) {
154: dsgn[j - 1] = FALSE_;
155: cancel[j - 1] = FALSE_;
156: scale = 0.;
157: i__1 = *nf - j;
158: for (i__ = 1; i__ <= i__1; ++i__) {
159: fval[i__] = fval[i__ + 1] - fval[i__];
160: if (fval[i__] == 0.) cancel[j - 1] = TRUE_;
162: /* Computing MAX */
163: d__2 = scale, d__3 = (d__1 = fval[i__], PetscAbsScalar(d__1));
164: scale = PetscMax(d__2,d__3);
165: }
167: /* Compute the estimates for the noise level. */
168: if (scale == 0.) stdv = 0.;
169: else {
170: stdv = 0.;
171: i__1 = *nf - j;
172: for (i__ = 1; i__ <= i__1; ++i__) {
173: /* Computing 2nd power */
174: d__1 = fval[i__] / scale;
175: stdv += d__1 * d__1;
176: }
177: stdv = scale * PetscSqrtScalar(stdv / (*nf - j));
178: }
179: eps[j] = const__[j - 1] * stdv;
180: /* Determine differences in sign. */
181: i__1 = *nf - j - 1;
182: for (i__ = 1; i__ <= i__1; ++i__) {
183: /* Computing MIN */
184: d__1 = fval[i__], d__2 = fval[i__ + 1];
185: /* Computing MAX */
186: d__3 = fval[i__], d__4 = fval[i__ + 1];
187: if (PetscMin(d__1,d__2) < 0. && PetscMax(d__3,d__4) > 0.) dsgn[j - 1] = TRUE_;
188: }
189: }
190: /* First requirement for detection of noise. */
191: dnoise = dsgn[3];
192: /* Check for h too small or too large. */
193: *info = 0;
194: if (f_max == f_min) *info = 2;
195: else /* if (complicated condition) */ {
196: /* Computing MIN */
197: d__1 = PetscAbsScalar(f_max), d__2 = PetscAbsScalar(f_min);
198: if (f_max - f_min > PetscMin(d__1,d__2) * .1) *info = 3;
199: }
200: if (*info != 0) return(0);
202: /* Determine the noise level. */
203: /* Computing MIN */
204: d__1 = PetscMin(eps[4],eps[5]);
205: emin = PetscMin(d__1,eps[6]);
207: /* Computing MAX */
208: d__1 = PetscMax(eps[4],eps[5]);
209: emax = PetscMax(d__1,eps[6]);
211: if (emax <= emin * 4 && dnoise) {
212: *fnoise = (eps[4] + eps[5] + eps[6]) / 3;
213: if (*fder2 != 0.) {
214: *info = 1;
215: *hopt = PetscSqrtScalar(*fnoise / PetscAbsScalar(*fder2)) * 1.68;
216: } else {
217: *info = 4;
218: *hopt = *h__ * 10;
219: }
220: return(0);
221: }
223: /* Computing MIN */
224: d__1 = PetscMin(eps[3],eps[4]);
225: emin = PetscMin(d__1,eps[5]);
227: /* Computing MAX */
228: d__1 = PetscMax(eps[3],eps[4]);
229: emax = PetscMax(d__1,eps[5]);
231: if (emax <= emin * 4 && dnoise) {
232: *fnoise = (eps[3] + eps[4] + eps[5]) / 3;
233: if (*fder2 != 0.) {
234: *info = 1;
235: *hopt = PetscSqrtScalar(*fnoise / PetscAbsScalar(*fder2)) * 1.68;
236: } else {
237: *info = 4;
238: *hopt = *h__ * 10;
239: }
240: return(0);
241: }
242: /* Noise not detected; decide if h is too small or too large. */
243: if (!cancel[3]) {
244: if (dsgn[3]) *info = 2;
245: else *info = 3;
246: return(0);
247: }
248: if (!cancel[2]) {
249: if (dsgn[2]) *info = 2;
250: else *info = 3;
251: return(0);
252: }
253: /* If there is cancelllation on the third and fourth column */
254: /* then h is too small */
255: *info = 2;
256: return(0);
257: /* if (cancel .or. dsgn(3)) then */
258: /* info = 2 */
259: /* else */
260: /* info = 3 */
261: /* end if */
262: } /* dnest_ */