piecewise symbolic function within a symbolic matrix

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Hallo, I would like to construct a matrix P whose elements depend on x (a vector that varies with time). Some elements of P are piecewise functions of x. The code is just to test whether P can be updated. Any help will be much appreciated.
sym x
P = sym(zeros(3,3)) %create empty symbolic matrix
P(1,1) = sym('1/(1+exp(-4.3*x(1)))')
P(2,1) = sym('0.2*x(2)')
P(3,1) = sym('0.4*sin(0.0192+x(3))')
P(1,2) = sym('1/(1+exp(11.8*x(2)))')
P(2,2) = .3435
P(3,2) = sym('.02 + (x(3)>=.04)*(.66*x(3))') %piecewise
x = [.5, .5, .1]
eval(P)
But I get an error due to the piecewise function (without it, P easily updates):
Error using sym/eval (line 11)
Error: Unbalanced or unexpected parenthesis or bracket.
Outside of the sym function, .02 + (x(3)>=.04)*(.66*x(3)) works all right.
I have also tried:
sym('piecewise([x(3)<.04,.02],[x(3)>=.04,0.02+0.66*x(3)])')
but still no go...I wonder what I am doing wrong? Thanks for your time

Accepted Answer

Star Strider
Star Strider on 8 Jul 2014
You may not be doing anything actually ‘wrong’, but eval may not be your best choice.
Replace it with:
vpa(P)
to get it to work without errors.
  5 Comments
Star Strider
Star Strider on 13 Nov 2014
My pleasure!
The sincerest expression of appreciation here on MATLAB answers is to Accept the answer that most closely solves your problem.
Walter Roberson
Walter Roberson on 23 Jan 2016
Inside the Symbolic Toolbox, the result of comparisons is true (a logical value) or false (a logical value) or FAIL (which is its own object type) . The results are not numeric 0 or numeric 1, so
sym('.02 + (x(3)>=.04)*(.66*x(3))')
will not do what is desired.

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