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How to calculate the syms with variable has the same name?

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wei zhang
wei zhang 2020-6-10
回答： Stephen23 2020-6-10
Hello,
I am writing a function with an augument to receive some expression, like ' a>0', ' b<0' and 'a>0&b<0'. There are variables named as "a" and "b" in the function's workspace. The augument to receive the expression is char class. How could I to calculate this expression in the function? Must I use "eval"? I have got a suggestion that I should not use "eval". I thought I could turn the char expression to syms with "str2sym". What should I do next? Thank you.
function myfun(exp,a,b)
% e.g. exp= 'a>0';
% 1st way : eval(exp)
% 2nd way(I prefer):
% exp1 = str2sym(exp);
% I don't know what to do next
end

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回答（1 个）

Stephen23
Stephen23 2020-6-10
function out = myfun(exp,a,b)
fun = str2func(sprintf('@(a,b)%s;',exp));
out = fun(a,b);
end
Tested:
>> myfun('a>0',3,2)
ans = 1
>> myfun('a>0&&b<0',3,2)
ans = 0

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