/* Program to calculate the inductance of a coil * * Reference: E. Jahnke and F. Emde, _Tables of Functions_, * 4th edition, Dover, 1945, pp 86-89. */double sin(), cos(), atan(), ellpe(), ellpk();double d;double l;double N;/* double PI = 3.14159265358979323846; */extern double PI;main(){double a, f, tana, sina, K, E, m, L, t;printf( "Self inductance of circular solenoidal coil\n" );loop:getnum( "diameter in centimeters", &d );if( d < 0.0 )	exit(0);  /* escape gracefully */getnum( "length in centimeters", &l );if( d < 0.0 )	exit(0);getnum( "total number of turns", &N );if( d < 0.0 )	exit(0);tana = d/l;        /* form factor */a = atan( tana );sina = sin(a);     /* modulus of the elliptic functions (k) */m = cos(a);        /* subroutine argument = 1 - k^2 */m = m * m;K = ellpk(m);E = ellpe(m);tana = tana * tana;  /* square of tan(a) */f = ((K + (tana - 1.0) * E)/sina  -  tana)/3.0;L = 4.e-9 * PI * N * N * d * f;printf( "L = %.4e Henries\n", L );goto loop;}/* Get value entered on keyboard */getnum( str, pd )char *str;double *pd;{char s[40];printf( "%s (%.10e) ? ", str, *pd );gets(s);if( s[0] != '\0' )	{	sscanf( s, "%lf", pd );	printf( "%.10e\n", *pd );	}}