% Biot-Savart demo for straight wire
% assumes that current is set to 4pi/mu_o

% test two different length wires (finite)
L = [1,10];
dz = 0.1;

% two separate meshes for the various length wires
z1 = -L(1):dz:L(1);
z2 = -L(2):dz:L(2);

% let's compare various distances from the wire
x = 0.1:0.05:1;
xe = x(1):.001:x(end); % fine mesh for exact case

% re-allocate B results for each length & each distance
B1 = zeros(length(x),1);
B2 = B1;

% loop over distances, & then also over each element dz
for h = 1:length(x)
    for k = 1:length(z1)
        B1(h) = B1(h) + dz * x(h) ./ (x(h)^2 + z1(k)^2).^(3/2);
    end
    for k = 1:length(z2)
        B2(h) = B2(h) + dz * x(h) ./ (x(h)^2 + z2(k)^2).^(3/2);
    end
end

% exact result is a simple step
B = 2./xe;

% plot the results
clf
plot(xe,B,'b-',x,B1,'ko',x,B2,'rd')
xlabel('x')
ylabel('B_y')
title('B-field from a straight wire')
legend('L = \infty',['L = ' num2str(L(1))],['L = ' num2str(L(2))])

return