error using sym/subs with logical operation

Hello,

here is my code

syms x1 x2
aa=x1 == 0 & x2 == 0
subs(aa, [0.5 0.5])

the result is

ans = 
    [ 1/2 == 0 & x2 == 0, 1/2 == 0 & x2 == 0]

I wanna get result like this

1/2==0 & 1/2==0

What's the problem?

Thanks.

Answer 1

[Stephan]

1

You only substitute x1 - you have to substitute them both. Try:

syms x1 x2
aa= x1 == 0 & x2 == 0
aa = subs(aa,[x1 x2], [0.5 0.5])

which results in:

aa =
 
1/2 == 0

2

Or use vectors, which doesnt work together with "&":

syms x1 x2
aa=[x1 == 0, x2 == 0]
aa = subs(aa,[x1 x2], [0.5 0.5])

result is:

aa =
 
[ 1/2 == 0, 1/2 == 0]

3

If you use 2 different numbers:

syms x1 x2
aa= x1 == 0 & x2 == 0
aa = subs(aa,[x1 x2], [0.5 0.6])

you get:

aa =
 
1/2 == 0 & 3/5 == 0

because Matlab can not simplify this, like it did in the first example.

[alice W]

thank you very much!

[Stephan]

my pleasure - please accept useful answers

[Stephen23]

+1 clear and useful answer