matlab函數求極值

函數的極值,1、一元函數的極值,函數命令：fminbnd,調用格式：x,feval,exitflag,output=fminbnd(fun,x1,x2,options),%求fun在區(qū)間(x1,x2)上的極值.返回值：x:函數fun在(x1,x2)內的極值點feval:求得函數的極值exitflag:exitflag0,函數收斂于解x處exitflag=0,已達最大迭代次數exiflagA=fsolve(myfsolve2,ones(3)%ones（3）初始矩陣，直全為1myfsolve2(A),4、數值積分,函數命令：quadquadlodbquad調用格式:q1=quad(fun,a,b,tol)%采用自適應Simpson算法計算積分q1=quadl(fun,a,b,tol)%采用自適應Lobatto算法計算積分q2=dblquad(fun,xmin,xmax,ymin,ymax,tol)%二重積分q3=triplequad(fun,xmin,xmax,ymin,ymax,zmin,zmax,tol)%三重積分,例1：求I=,.,(1)利用quad,quadl計算formatlongI=quad(exp(-x.2),0,1,1e-8)Il=quadl(exp(-x.2),0,1,1e-8)I=0.74682413285445Il=0.74682413398845,(2)采用編程計算:,functionI=myquad1(a,b,n)x=linspace(a,b,n);%把ab區(qū)間平均分成n等份y=exp(-x.2)*(b-a)/n;%高底=每個取邊梯形的面積I=sum(y);I1=myquad1(0,1,10000)I2=myquad1(0,1,100000)I1=0.74681784375801I2=0.74682350396218,例2：計算,利用dblquads1=dblquad(x.y,0,1,1,2),%被積函數寫成數組的形式db_(double)二重積分，即兩次積分s1=0.40546626724351s2=dblquad(x,y)x.y,0,1,1,2)%采用匿名函數表示被積函數xy的區(qū)間s2=0.40546626724351s3=dblquad(inline(x.y),0,1,1,2)s3=0.40546626724351,求s1=,s2=,s3=,例3：,symsxx符號變量f1=1/(1+x2);f2=1/(x2+2*x+3);f3=1/(x2+2*x-3);s1=int(f1,1,inf)1到正無窮s2=int(f2,-inf,inf)int符號積分s3=int(f3,-inf,inf)s1=1/4*pis2=1/2*pi*2(1/2)s3=NaN不確定的結果,s4=quad(1./(1+x.2),1,inf)%quad只能計算閉型積分Warning:InfiniteorNot-a-Numberfunctionvalueencountered.Inquadat95s4=NaNs5=quad(1./(1+x.2),1,10)