How to use str2func to replace eval command?

2013 12 4
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更新时间：2013 12 4
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0 个投票

I want user to enter a parametrized function in terms of t. Is there a way that I can have an input function instead of using '' and eval?
t = linspace(0.001,2,1000);
T = t;
x_e = 't.^3';
y_e = 'exp(t)';
z_e = 'cos(10*t)';
x = eval(x_e);
y = eval(y_e);
z = eval(z_e);

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Walter Roberson
Walter Roberson 2013-12-4
编辑：Walter Roberson 2013-12-4

0 个投票

fx = str2func(['@(t) ', x_e]);
x = fx(t);
Just like the examples in http://www.mathworks.com/help/matlab/ref/str2func.html

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Matthew
Matthew 2013-12-4
编辑：Walter Roberson 2013-12-4
I tried your way and it gave me an error
This is my code
t = linspace(0.001,2,1000);
T = t;
x_e = input ('x_e');
y_e = input ('y_e');
z_e = input ('z_e');
fx = str2func(['@(t) ', x_e], 't');
x = fx(t);
fy = str2func(['@(t) ', y_e], 't');
y = fy(t);
fz = str2func(['@(t) ', z_e], 't');
z = fz(t);
and this is what the command window said
Error using str2func
Too many input arguments.
Error in test (line 6)
fx = str2func(['@(t) ', x_e], 't');
Thx
Walter Roberson
Walter Roberson 2013-12-4
Sorry, corrected. After I put in the bad code I checked the documentation and then forgot to fix the mistake before sending.
Andrei Bobrov
Andrei Bobrov 2013-12-4
Hi Matthew and Walter!
t = linspace(0.001,2,1000);
x_e = 't.^3';
y_e = 'exp(t)';
z_e = 'cos(10*t)';
funs = cellfun(@str2func,strcat('@(t),{x_e,y_e,z_e}),'un',0);
rez = cellfun(@(q)q(t),funs,'un',0);
[x,y,z] = rez{:};

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更多回答（1 个）

Andrei Bobrov
Andrei Bobrov 2013-12-4

0 个投票

t = linspace(0.001,2,1000);
x_e = 't^3';
y_e = 'exp(t)';
z_e = 'cos(10*t)';
funs = arrayfun(@matlabFunction,sym({x_e,y_e,z_e}),'un',0);
rez = cellfun(@(q)q(t),funs,'un',0);
[x,y,z] = rez{:};

2 个评论
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Walter Roberson
Walter Roberson 2013-12-4
编辑：Walter Roberson 2013-12-4
Notice here that Andrei had to change
x_e = 't.^3';
to
x_e = 't^3';
This is because sym() interprets strings as being in MuPAD language, which is slightly different than MATLAB itself. str2func() uses MATLAB language. matlabFunction() knows to convert MuPAD symbols into MATLAB language.
Matthew
Matthew 2013-12-4
Thanks I tried both of your ways and both of them work.

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