var_t

function [position_error, emf ] = var_t( delta_t )
rho=26570;

phi_1=(pi/2)*0;
theta_1=(0*pi);

A1=rho*cos(phi_1)*cos(theta_1);
B1=rho*cos(phi_1)*sin(theta_1);
C1=rho*sin(phi_1);

phi_2=(pi/8);
theta_2=((2/3)*pi);

A2=rho*cos(phi_2)*cos(theta_2);
B2=rho*cos(phi_2)*sin(theta_2);
C2=rho*sin(phi_2);

phi_3=(pi/4);
theta_3=((4/3)*pi);

A3=rho*cos(phi_3)*cos(theta_3);
B3=rho*cos(phi_3)*sin(theta_3);
C3=rho*sin(phi_3);

phi_4=(pi/2);
theta_4=(2*pi);

A4=rho*cos(phi_4)*cos(theta_4);
B4=rho*cos(phi_4)*sin(theta_4);
C4=rho*sin(phi_4);

x=0;
y=0;
z=6370;

c=299792.458;

R1=s_r(A1,B1,C1);
t1=trav_time(R1)+delta_t;

R2=s_r(A2,B2,C2);
t2=trav_time(R2)-delta_t;

R3=s_r(A3,B3,C3);
t3=trav_time(R3)+delta_t;

R4=s_r(A4,B4,C4);
t4=trav_time(R4)-delta_t;

[x1,y1,z1]=gps(A1,B1,C1,A2,B2,C2,A3,B3,C3,A4,B4,C4,t1,t2,t3,t4);

sup_norm_xyz=sup_norm(x1,y1,z1);

ct=c*delta_t;

position_error=sup_norm_xyz

emf=sup_norm_xyz/ct

end

Not enough input arguments.

Error in var_t (line 39)
t1=trav_time(R1)+delta_t;