多元函数在某一点的函数值用matlab的哪个函数命令 求解
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多元函数在某一点的函数值用matlab的哪个函数命令 求解
多元函数在某一点的函数值用matlab的哪个函数命令 求解
多元函数在某一点的函数值用matlab的哪个函数命令 求解
还是回答你的那个例子,你需要用subs函数将符号运算转化成常数运算,
subs(z,{x,y},{2,4})
关于subs的具体信息可以参考matlab的帮助文件
SUBS Symbolic substitution.
SUBS(S) replaces all the variables in the symbolic expression S with
values obtained from the calling function, or the MATLAB workspace.
SUBS(S,NEW) replaces the free symbolic variable in S with NEW.
SUBS(S,OLD,NEW) replaces OLD with NEW in the symbolic expression S.
OLD is a symbolic variable, a string representing a variable name, or
a string (quoted) expression. NEW is a symbolic or numeric variable
or expression.
If OLD and NEW are vectors or arrays of the same size, each element
of OLD is replaced by the corresponding element of NEW. If S and OLD
are scalars and NEW is an array or cell array, the scalars are expanded
to produce an array result. If NEW is a cell array of numeric matrices,
the substitutions are performed elementwise (i.e., subs(x*y,{x,y},{A,B})
returns A.*B when A and B are numeric).
If SUBS(S,OLD,NEW) does not change S, then SUBS(S,NEW,OLD) is tried.
This provides backwards compatibility with previous versions and
eliminates the need to remember the order of the arguments.
SUBS(S,OLD,NEW,0) does not switch the arguments if S does not change.
Multiple Substitutions:
subs(cos(a)+sin(b),{a,b},[sym('alpha'),2]) or
subs(cos(a)+sin(b),{a,b},{sym('alpha'),2}) returns
cos(alpha)+sin(2)
Scalar Expansion Case:
subs(exp(a*t),'a',-magic(2)) returns
[ exp(-t), exp(-3*t)]
[ exp(-4*t), exp(-2*t)]
Multiple Scalar Expansion:
subs(x*y,{x,y},{[0 1;-1 0],[1 -1;-2 1]}) returns
[ 0, -1]
[ 2, 0]
不知道你想要问什么？写出函数的表达式来，将（x，y）赋值给表达式就有了。有万能的固定函数吗？