> restart;
> # SECANT ALGORITHM 2.4
> #
> # 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.
> alg024 := proc() local F, OK, P0, P1, TOL, NO, FLAG, NAME, OUP, F0, I, F1, P, FP;
> printf(`This is the Secant Method\n`);
> printf(`Input the function F(x) in terms of x\n`);
> printf(`For example: cos(x)\n`);
> F := scanf(`%a`)[1];
> F := unapply(F,x);
> OK := FALSE;
> while OK = FALSE do
> printf(`Input initial approximations P0 and P1 separated by a blank\n`);
> P0 := scanf(`%f`)[1]; 
> P1 := scanf(`%f`)[1];
> if P0 = P1 then
> printf(`P0 cannot equal P1\n`);
> else
> OK := TRUE;
> fi;
> od;
> OK := FALSE;
> while OK = FALSE do
> printf(`Input tolerance\n`);
> TOL := scanf(`%f`)[1];
> if TOL <= 0 then
> printf(`Tolerance must be positive\n`);
> else 
> OK := TRUE;
> fi;
> od;
> OK := FALSE;
> while OK = FALSE do
> printf(`Input maximum number of iterations - no decimal point\n`);
> NO := scanf(`%d`)[1];
> if NO <= 0 then
> printf(`Must be positive integer\n`);
> else 
> OK := TRUE;
> fi;
> od;
> if OK = TRUE then
> printf(`Select output destination\n`);
> printf(`1. Screen\n`);
> printf(`2. Text file\n`);
> printf(`Enter 1 or 2\n`);
> FLAG := scanf(`%d`)[1];
> if FLAG = 2 then
> printf(`Input the file name in the form - drive:\\name.ext\n`);
> printf(`For example:   A:\\OUTPUT.DTA\n`);
> NAME := scanf(`%s`)[1];
> OUP := fopen(NAME,WRITE,TEXT);
> else
> OUP := default;
> fi;
> printf(`Select amount of output\n`);
> printf(`1. Answer only\n`);
> printf(`2. All intermediate approximations\n`);
> printf(`Enter 1 or 2\n`);
> FLAG := scanf(`%d`)[1];
> fprintf(OUP, `Secant Method\n`);
> if FLAG = 2 then
> fprintf(OUP, `  I    P                 F(P)\n`);
> fi;
> # Step 1
> I := 2;
> F0 := F(P0);
> F1 := F(P1);
> OK := TRUE;
> # Step 2
> while I <= NO and OK = TRUE do  
> # Step 3
> # Compute P(I)
> P := P1-F1*(P1-P0)/(F1-F0);
> FP := F(P);
> if FLAG = 2 then
> fprintf(OUP,`%3d   %15.8e   %15.8e\n`,I,P,FP);
> fi;
> # Step 4
> if abs(P-P1) < TOL then
> # 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 = %d\n`,I);
> fprintf(OUP,`Tolerance = %14.8e\n`,TOL);
> OK := FALSE;
> # Step 5
> else
> I := I+1;
> # Step 6
> # Update P0, F0, P1, F1
> P0 := P1;
> F0 := F1;
> P1 := P;
> F1 := FP;
> fi;
> od;
> if OK = TRUE then
> # Step 7
> # Procedure completed unsuccessfully
> fprintf(OUP,`\nIteration number %d`,NO);
> fprintf(OUP,` gave approximation %12.8f\n`,P);
> fprintf(OUP,`with F(P) = %12.8f not within tolerance  %15.8e\n`,FP,TOL);
> fi;
> if OUP <> default then
> fclose(OUP):
> printf(`Output file %s created successfully`,NAME);
> fi;
> fi;
> RETURN(0);
> end;
> alg024();