作业帮Matlab中subs函数
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Matlab中subs函数
syms x y;
subs(x*y, {x, y}, {[0 1; -1 0], [1 -1; -2 1]})
x与y是'*',不是'.*'啊,为什么会得到这个结果
ans = 0 -1
2 0
syms x y;
subs(x*y, {x, y}, {[0 1; -1 0], [1 -1; -2 1]})
x与y是'*',不是'.*'啊,为什么会得到这个结果
ans = 0 -1
2 0
这里subs的替换换就是元素替换,没有矩阵替换后执行矩阵运算
你要进行矩阵运算可以这样写
>> x=sym([0 1;-1 0]);
>> y=sym([1 -1;-2 1]);
>> x*y
ans =
[ -2,1]
[ -1,1]
再问： 我知道这些，我的问题是为什么会出现这个结果？
再答： subs的替换就是元素替换，就算是带入矩阵也是执行元素运算，subs程序就是这样写的啊 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]
你要进行矩阵运算可以这样写
>> x=sym([0 1;-1 0]);
>> y=sym([1 -1;-2 1]);
>> x*y
ans =
[ -2,1]
[ -1,1]
再问： 我知道这些，我的问题是为什么会出现这个结果？
再答： subs的替换就是元素替换，就算是带入矩阵也是执行元素运算，subs程序就是这样写的啊 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]