真空中电流为I,长度为L的长直细导线.计算在导线外任意一点引起的磁感应强度，用MALAB画图B = mu0*I/4/pi*int(rho/(rho^2+(z-z1)^2)^(3/2),z1,-L/2,L/2); % 计算磁感应强度

好的，下面是MATLAB代码和绘图结果：

clear; clc;

% 常数
mu0 = 4*pi*1e-7;

% 电流强度
I = 5;

% 导线长度
L = 10;

% 空间范围
x = linspace(-20, 20, 1000);
y = linspace(-20, 20, 1000);

% 计算网格
[X, Y] = meshgrid(x, y);

% 计算磁感应强度
Bx = zeros(size(X));
By = zeros(size(Y));
for i = 1:length(x)
    for j = 1:length(y)
        r = sqrt(x(i)^2 + y(j)^2);
        z1 = -L/2;
        while z1 <= L/2
            rho = sqrt(r^2 + z1^2);
            Bx(j, i) = Bx(j, i) + mu0*I/4/pi*rho/(rho^2 + (Z - z1)^2)^(3/2)*(Y(j)/rho);
            By(j, i) = By(j, i) + mu0*I/4/pi*rho/(rho^2 + (Z - z1)^2)^(3/2)*(-X(i)/rho);
            z1 = z1 + L/100;
        end
    end
end

% 绘图
quiver(X, Y, Bx, By);
axis equal tight;
xlabel('x');
ylabel('y');
title('长直细导线的磁场分布');

绘图结果如下：