Question

matlab 区间是个函数形式，如何画出分段函数的三维曲面图

SigmaP=@(b)(382.6912.*(b+2)+57.6757.*(1+b))./(1.4487.*(2.*b+2)+1.2756.*(2-b));
R=@(b)(1.2963./((382.6912.*(b+2)+57.6757.*(1+b))./(1.4487.*(2.*b+2)+1.2756.*(2-b))-100)).^(1/3);
Sigmare=@(b,r)100+(-100+((382.6912.*(b+2)+57.6757.*(1+b))./(1.4487.*(2.*b+2)+1.2756.*(2-b))))...
.*((1.2963./((382.6912.*(b+2)+57.6757.*(1+b))./(1.4487.*(2.*b+2)+1.2756.*(2-b))-100)).^(1/3)./r).^3;
Sigmarp=@(b,r)-115.3514.*(1+b)./(5.1025-2.8975.*(1+b))...
+(((1.2963./((382.6912.*(b+2)+57.6757.*(1+b))./(1.4487.*(2.*b+2)+1.2756.*(2-b))-100)).^(1/3)./r)...
.^((5.1025-2.8975.*(1+b))./(2.5512+1.2756.*b))).*((382.6912.*(b+2)+57.6757.*(1+b))./(1.4487.*(2.*b+2)+1.2756.*(2-b))+(115.3514.*(1+b)./(5.1025-2.8975.*(1+b))));

如上，Sigmar分两部分：Sigmare和Sigmarp，均是关于b和r的函数，b取值为0到1；对于Sigmare，r取值为R到1，对于Sigmarp，r取值是0到R。而R又是一个关于b的函数，所以我不知道怎么取分段函数。
最后需要画出Sigmar在b为0到1，r为0到1的三维曲线图

Answer 1

clear;
R=@(b)(1.2963./((382.6912.*(b+2)+57.6757.*(1+b))./(1.4487.*(2.*b+2)+1.2756.*(2-b))-100)).^(1/3);
Sigmare=@(b,r)100+(-100+((382.6912.*(b+2)+57.6757.*(1+b))./(1.4487.*(2.*b+2)+1.2756.*(2-b))))...
.*((1.2963./((382.6912.*(b+2)+57.6757.*(1+b))./(1.4487.*(2.*b+2)+1.2756.*(2-b))-100)).^(1/3)./r).^3;
Sigmarp=@(b,r)-115.3514.*(1+b)./(5.1025-2.8975.*(1+b))...
+(((1.2963./((382.6912.*(b+2)+57.6757.*(1+b))./(1.4487.*(2.*b+2)+1.2756.*(2-b))-100)).^(1/3)./r)...
.^((5.1025-2.8975.*(1+b))./(2.5512+1.2756.*b))).*((382.6912.*(b+2)+57.6757.*(1+b))./(1.4487.*(2.*b+2)+1.2756.*(2-b))+(115.3514.*(1+b)./(5.1025-2.8975.*(1+b))));
Sigmar=@(b,r)Sigmare(b,r).*(r>R(b))+Sigmarp(b,r).*(r<=R(b));
t=linspace(0,1);
[b,r]=meshgrid(t);
mesh(b,r,Sigmar(b,r));
hold on 
plot3(t,R(t),Sigmar(t,R(t)),'w:','linewidth',3)
xlabel('b');ylabel('r');zlabel('Sigmar(b,r)');

SigmaP这个函数没用的吧

追问

先谢谢大神了，您说SigmaP这个函数没用，为什么？
还有，Sigmar=@(b,r)Sigmare(b,r).*(r>R(b))+Sigmarp(b,r).*(r<=R(b));这步怎么理解？
麻烦您啦，我比较笨

追答

你的原始问题里压根没提到SigmaP这个函数啊，也没看到哪里用了啊