[MATLAB基础] d = sqrt((xd-xb).^2+(yd-yb).^2)报错

[尚云520]

function [xc , yc , phi2 , phi3] = s_RRR(xb , yb , xd , yd , i2 , i3 , m )
d = sqrt((xd-xb).^2+(yd-yb).^2);
if (d>(i2 - i3))||(d<abs(i2 - i3))
errordlg('不能组装');
else
delta = atan((yd - yb)./(xd - xb));
gama = acos((d.^2 + i2.^2 - i3.^2)./(2 * d * i2));
phi2 = delta + m * gama;
xc = xb + i2.*cos(phi2);
yc = yb + i2.*sin(phi2);
phi3 = atan((yc - yd),(xc - xd));
end

报错：
??? Input argument "xd" is undefined.

Error in ==> s_RRR at 2
d = sqrt((xd-xb).^2+(yd-yb).^2);

这是为什么呢？请教高人