I am trying to use the biot savart law to calculate the magnetic field of a given object. I have got to the stage where I have calculated I*dl and R/R^2 separately (doing this in matlab. The problem is where I come to the cross product. If I have a uniform current, the values of the current vector would be zero where there is no cable. i.e. if I have a current loop of uniform current = 1, anywhere outside or inside the current loop, the value of I*dl = 0 right? So if this is correct, when I take the cross product of I*dl and R/R^2, I will be crossing a vector of value 0, with the R/R^2 in places outisde of the loop, which leads to a value of 0. Although, the magnetic field due to the current is only 0 is the distance goes to infinity, so I cannot have a space in the vicinity of the wire with magnetic field = 0. What am I not understanding here?