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[c] <math.h>

  1. Oct 31, 2006 #1
    Hello guys. I'm having some problems when compiling some C programs. I can't troubleshoot them since I'm not very proficient with C. But it seems that this error comes from the math.h library, maybe the include is different for Linux.

    This is the error i'm getting:
    Kareem@Kareem:~/prog/secant$ cc main.c
    /tmp/cciW3fYU.o(.text+0x219): In function `F':
    : undefined reference to `cos'
    collect2: ld returned 1 exit status

    this is the code:

    Code (Text):
    *   To find a solution to the equation f(x) = 0
    *   given initial approximations p0 and p1:
    *   INPUT:   initial approximation p0, p1; tolerance TOL;
    *            maximum number of iterations N0.
    *   OUTPUT:  approximate solution p or
    *            a message that the algorithm fails.

    #define true 1
    #define false 0

       double P0,F0,P1,F1,P,FP,TOL;
       int I,NO,OK,FLAG;
       FILE *OUP[1];

       double absval(double);
       double F(double);
       void INPUT(int *, double *, double *, double *, int *);
       void OUTPUT(FILE **, int *);

       INPUT(&OK, &P0, &P1, &TOL, &NO);
       if (OK) {
          OUTPUT(OUP, &FLAG);
          /* STEP 1 */
          I = 2;      
          F0 = F(P0);
          F1 = F(P1);
          OK = true;                                
          /* STEP 2 */
          while ((I<=NO) && OK) {  
         /* STEP 3 */
         /* compute P(I) */
         P = P1 - F1 * (P1 - P0) / (F1 - F0);

         /* STEP 4 */  
         FP = F(P);  
         if (FLAG == 2) fprintf(*OUP,"%3d   %15.8e   %15.8e \n",I,P,FP);
         if (absval(P - P1) < TOL) {
            /* procedure completed successfully */
            fprintf(*OUP,"\nApproximate solution P = %12.8f\n",P);
            fprintf(*OUP,"with F(P) = %12.8f\n",FP);
            fprintf(*OUP,"Number of iterations = %3d",I);
            fprintf(*OUP,"    Tolerance = %14.8e\n",TOL);
            OK = false;
         else {
            /* STEP 5 */
            /* STEP 6 */
            /* update P0, F0, P1, F1 */
            P0 = P1;
            F0 = F1;
            P1 = P;
            F1 = FP;
          if (OK) {
         /* STEP 7 */
         /* procedure completed unsuccessfully */      
         fprintf(*OUP,"\nIteration number %3d",NO);
         fprintf(*OUP," gave approximation %12.8f\n",P);
         fprintf(*OUP,"F(P) = %12.8f not within tolerance : %15.8e\n",FP,TOL);
       return 0;

    /* Change function F for a new problem */
    double F(double X)
       double f;

       f = cos(X) - X;
       return f;

    void INPUT(int *OK, double *P0, double *P1, double *TOL, int *NO)
       char AA;

       printf("This is the Secant Method.\n");
       printf("Has the function F been created in the program immediately preceding\n");
       printf("the INPUT function?\n");
       printf("Enter Y or N\n");
       if ((AA == 'Y') || (AA == 'y')) {
          *OK = false;
          while (!(*OK)) {
         printf("Input initial approximations P0 and P1 separated by blank\n");
         scanf("%lf %lf", P0, P1);
         if (*P0 == *P1) printf("P0 cannot equal P1\n");
         else *OK = true;
          *OK = false;
          while(!(*OK)) {
         printf("Input tolerance\n");
         scanf("%lf", TOL);
         if (*TOL <= 0.0) printf("Tolerance must be positive\n");
         else *OK = true;
          *OK = false;
          while (!(*OK)) {
         printf("Input maximum number of iterations - no decimal point\n");
         scanf("%d", NO);
         if (*NO <= 0) printf("Must be positive integer\n");
         else *OK = true;
       else {
          printf("The program will end so that the function F can be created\n");
          *OK = false;

    void OUTPUT(FILE **OUP, int *FLAG)
       char NAME[30];

       printf("Select output destination\n");
       printf("1. Screen\n");
       printf("2. Text file\n");
       printf("Enter 1 or 2\n");
       scanf("%d", FLAG);
       if (*FLAG == 2) {
          printf("Input the file name in the form - drive:name.ext\n");
          printf("For example:   A:OUTPUT.DTA\n");
          scanf("%s", NAME);
          *OUP = fopen(NAME, "w");
       else *OUP = stdout;
       printf("Select amount of output\n");
       printf("1. Answer only\n");
       printf("2. All intermeditate approximations\n");
       printf("Enter 1 or 2\n");
       scanf("%d", FLAG);
       fprintf(*OUP,"Secant Method\n");
       if (*FLAG == 2) fprintf(*OUP, "  I                 P              F(P)\n");

    /* Absolute Value Function */
    double absval(double val)
       if (val >= 0) return val;
       else return -val;
  2. jcsd
  3. Oct 31, 2006 #2


    User Avatar

    Staff: Mentor

    So is cos() in your copy of math.h? It's in my VC++ Include folder's math.h. Is the compiler complaining about anything in stdio.h? I usually see a space after the #include statement for those two .h files, and don't know if not having a space will make the compiler not like those include definitions.
  4. Oct 31, 2006 #3
    I've tried with different algorithms, and they all complain about some math functions like cos(),sin() and tan().

    absval() might also be in the math.h library, but the compiler isn't complaining about it. It's not complaining about stdio.h. I tried including spaces betweeh # and include, still didn't work.
  5. Oct 31, 2006 #4


    User Avatar
    Science Advisor
    Homework Helper

    You might need to use "-lm" or something similar when you compile.
  6. Oct 31, 2006 #5
    Oh yeah right it worked...used cc -lm filename.c -o filename.

    thanks NateTG :)
  7. Oct 31, 2006 #6
    btw why is it necessary to use the -lm option?
  8. Oct 31, 2006 #7


    User Avatar
    Science Advisor
    Homework Helper

  9. Oct 31, 2006 #8
    Thanks for the link, very useful. Do you guys recommend any editor other than VI? One that indents and stuff like that.
  10. Oct 31, 2006 #9


    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    vim does indenting, and colors too. I don't remember how to activate the feature, though. (these days, vi is most likely simply an alias for vim)

    xemacs (and emacs) seem to be popular editors too.

    (I use the above two most often. I tend to use vim for quick edits, and xemacs for more extended editing sessions)

    If you're willing to go download stuff, eclipse is a very nice IDE. The trouble is that it's designed for java -- it has a plugin for C/C++, but I don't know how good it is.

    There are interesting editors that maybe others can say something about.
  11. Nov 1, 2006 #10
    I use Eclipse's CDT plugin (for C/C++) and its pretty nice. I use Eclipse for a lot of Java developement though so I was already familiar with it before I started using CDT.
  12. Nov 8, 2006 #11
    Thanks for the recommendations. I'm using gedit right now, it's pretty nice and simple.
  13. Nov 9, 2006 #12


    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    I use nedit.

    - Warren
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