C 代码 使用平分法寻求方程 F（X）=0 的解 在用户提供的符号间隔 [A，B] 更改内.rar

# include <stdlib.h> # include <stdio.h> # include <time.h> # include "bisection_rc.h" /******************************************************************************/ double bisection_rc ( double *a, double *b, double fx, int *job ) /******************************************************************************/ /* Purpose: BISECTION_RC seeks a zero of f(x) in a change of sign interval. Discussion: The bisection method is used. This routine uses reverse communication, so that the function is always evaluated in the calling program. On the first call, the user sets JOB = 0, and the values of A and B. Thereafter, the user checks the returned value of JOB and follows directions. Licensing: This code is distributed under the GNU LGPL license. Modified: 14 January 2013 Author: John Burkardt Parameters: Input/output, double *A, *B, the endpoints of the change of sign interval. These values will change from call to call as the interval size is reduced. Input, double FX, the function value at the point X returned on the previous call. On the first call, FX is ignored. Input/output, int *JOB, a communication flag. The user sets JOB to 0 before the first call. Thereafter, the program controls setting the value of JOB, whose output values mean: Output, double BISECTION_RC, a point X at which the function is to be evaluated. */ { static double fa; static double fb; static int state; double x; static double x_local; if ( *job == 0 ) { fa = 0.0; fb = 0.0; state = 1; x = *a; *job = 1; } else if ( state == 1 ) { fa = fx; x = *b; state = 2; } else if ( state == 2 ) { fb = fx; if ( r8_sign ( fa ) == r8_sign ( fb ) ) { fprintf ( stderr, "\n" ); fprintf ( stderr, "BISECTION_RC - Fatal error!\n" ); fprintf ( stderr, " F(A) and F(B) have the same sign.\n" ); exit ( 1 ); } x = ( *a + *b ) / 2.0; state = 3; } else { if ( r8_sign ( fx ) == r8_sign ( fa ) ) { *a = x_local; fa = fx; } else { *b = x_local; fb = fx; } x = ( *a + *b ) / 2.0; state = 3; } x_local = x; return x; } /******************************************************************************/ double r8_sign ( double x ) /******************************************************************************/ /* Purpose: R8_SIGN returns the sign of an R8. Licensing: This code is distributed under the GNU LGPL license. Modified: 08 May 2006 Author: John Burkardt Parameters: Input, double X, the number whose sign is desired. Output, double R8_SIGN, the sign of X. */ { double value; if ( x < 0.0 ) { value = - 1.0; } else { value = + 1.0; } return value; } /******************************************************************************/ void timestamp ( void ) /******************************************************************************/ /* Purpose: TIMESTAMP prints the current YMDHMS date as a time stamp. Example: 31 May 2001 09:45:54 AM Licensing: This code is distributed under the GNU LGPL license. Modified: 24 September 2003 Author: John Burkardt Parameters: None */ { # define TIME_SIZE 40 static char time_buffer[TIME_SIZE]; const struct tm *tm; time_t now; now = time ( NULL ); tm = localtime ( &now ); strftime ( time_buffer, TIME_SIZE, "%d %B %Y %I:%M:%S %p", tm ); fprintf ( stdout, "%s\n", time_buffer ); return; # undef TIME_SIZE }