matlab函数求极值

函数的极值,1、一元函数的极值,函数命令：fminbnd,调用格式：x,feval,exitflag,output=fminbnd(fun,x1,x2,options),%求fun在区间(x1,x2)上的极值.返回值：x:函数fun在(x1,x2)内的极值点feval:求得函数的极值exitflag:exitflag0,函数收敛于解x处exitflag=0,已达最大迭代次数exiflagA=fsolve(myfsolve2,ones(3)%ones（3）初始矩阵，直全为1myfsolve2(A),4、数值积分,函数命令：quadquadlodbquad调用格式:q1=quad(fun,a,b,tol)%采用自适应Simpson算法计算积分q1=quadl(fun,a,b,tol)%采用自适应Lobatto算法计算积分q2=dblquad(fun,xmin,xmax,ymin,ymax,tol)%二重积分q3=triplequad(fun,xmin,xmax,ymin,ymax,zmin,zmax,tol)%三重积分,例1：求I=,.,(1)利用quad,quadl计算formatlongI=quad(exp(-x.2),0,1,1e-8)Il=quadl(exp(-x.2),0,1,1e-8)I=0.74682413285445Il=0.74682413398845,(2)采用编程计算:,functionI=myquad1(a,b,n)x=linspace(a,b,n);%把ab区间平均分成n等份y=exp(-x.2)*(b-a)/n;%高底=每个取边梯形的面积I=sum(y);I1=myquad1(0,1,10000)I2=myquad1(0,1,100000)I1=0.74681784375801I2=0.74682350396218,例2：计算,利用dblquads1=dblquad(x.y,0,1,1,2),%被积函数写成数组的形式db_(double)二重积分，即两次积分s1=0.40546626724351s2=dblquad(x,y)x.y,0,1,1,2)%采用匿名函数表示被积函数xy的区间s2=0.40546626724351s3=dblquad(inline(x.y),0,1,1,2)s3=0.40546626724351,求s1=,s2=,s3=,例3：,symsxx符号变量f1=1/(1+x2);f2=1/(x2+2*x+3);f3=1/(x2+2*x-3);s1=int(f1,1,inf)1到正无穷s2=int(f2,-inf,inf)int符号积分s3=int(f3,-inf,inf)s1=1/4*pis2=1/2*pi*2(1/2)s3=NaN不确定的结果,s4=quad(1./(1+x.2),1,inf)%quad只能计算闭型积分Warning:InfiniteorNot-a-Numberfunctionvalueencountered.Inquadat95s4=NaNs5=quad(1./(1+x.2),1,10)