Need help with symbolic variables (if else statement)

3 次查看（过去 30 天）

Akbar 2018-7-13

编辑： Akbar 2018-7-18

if a > 10^-8 
switch1 = b; 
else 
switch1 = 0; 
end

i get the following error:

Conversion to logical from sym is not possible.

at line:

if a > 10^-8

I Need the above code to work with symbolic variables.

Akbar 2018-7-13

Just one number

Adam Danz 2018-7-13

编辑：Adam Danz 2018-7-13

Ok, see answers. If 'a' must be 'sym' Walter's answer is best. If 'a' can be converted to 'double', see my answer.

Walter Roberson 2018-7-13

You need to use piecewise() for this purpose.

Adam Danz 2018-7-13

According to your comments, 'a' is a symbol symbolizing a scalar number. If that's the case, you can convert 'a' to numerical.

    a = sym('3.14159'); 
    a = double(a);   % Convert to double
    if a > 10^-8 
       ...
    else 
       ...
    end

If you prefer to keep 'a' in the sym class, use Walter's answer.

Walter Roberson 2018-7-17

Sorry, I only answer public questions.

Akbar 2018-7-18

编辑：Akbar 2018-7-18

Ok. I have just solved my issue by substituting if else statement with tanh().

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