2楼: Originally posted by dbb627 at 2011-11-30 22:48:21:
命令窗口输入
fplot(@objfun,[-10 10])
或者
把函数改保存
Function y=objfun(x)

y=x.^2+5*x+20;

然后在命令窗口输入
x=-10:0.1:10;
plot(x,objfun(x))
[ Last edited by dbb627 on 2011-11-30 at ...

4楼: Originally posted by dbb627 at 2011-11-30 23:30:05:
你的two_min是否存在了当前工作目录下面，
function y = two_min(x)
if x<=20
    y = -exp(-(x/20).^2);
else
    y = -exp(-1)+(x-20).*(x-22);
end

function y=two_min(x)
y=zeros(size(x));  %定义y与x尺寸相同
ind=(x<=20);      %返回一个logic型
y(ind)=-exp(-(x(ind)/20).^2);
ind=(x>20);
y(ind)= -exp(-1)+(x(ind)-20).*(x-22);

function y=two_min(x)
y=zeros(size(x));  %定 ... [/quote]


最后一句再改一下。
[code]y(ind)= -exp(-1)+(x(ind)-20).*(x(ind)-22);

4楼: Originally posted by dbb627 at 2011-11-30 23:30:05:
你的two_min是否存在了当前工作目录下面，
function y = two_min(x)
if x<=20
    y = -exp(-(x/20).^2);
else
    y = -exp(-1)+(x-20).*(x-22);
end

6楼: Originally posted by baby_wolf at 2011-12-01 01:18:41:
最后一句再改一下。

CODE:

y(ind)= -exp(-1)+(x(ind)-20).*(x(ind)-22);

8楼: Originally posted by zongshengl at 2011-12-01 10:29:51:
谢谢！问题解决了

我还有个疑问：（1）是不是分段函数都这样写？
（2）如果不是分段函数是不是就不用这样写了？

非常感谢

x=-1:0.02:1;
y=-exp(10.5*(x+0.5)).*( x<-0.5 )+...
    (exp(3.51*(x+0.5))-2*exp(-3.51*(x+0.5))).*(x>-0.5&x<0.5)...
    -exp(10.5*(x+0.5)).*(x>0.5);
plot(x,y)
figure;semilogy(x,y)

9楼: Originally posted by dbb627 at 2011-12-01 10:37:16:
分段函数有很简单的写法，不用那么复杂
y=-exp(10.5*(x+0.5)) x<-0.5
y =exp(3.51*(x0.5))-2*exp(-3.51*(x+0.5))   (-0.5,0.5)
y=-exp(10.5*(x+0.5))    x>0.5

[code]
x=-1:0.02:1;
y=-exp(10.5 ...