对数坐标曲线：
clear
clc
x=0:0.1:2*pi;
y=sin(x);
subplot(2,2,1)
plot(x,y)
xlabel('x1');
ylabel('y1');
grid on
subplot(2,2,2)
semilogx(x,y)
xlabel('x2');
ylabel('y2');
grid on
subplot(2,2,3)
semilogy(x,y)
xlabel('x3');
ylabel('y3');
grid on
subplot(2,2,4)
loglog(x,y)
xlabel('x4');
ylabel('y4');
grid on
