Hello,


You can use intermediate variables using multiple expressions with the comma separator:

>>> f=ot.SymbolicFunction(['x1', 'x2', 'x3'], ['x3=x1+x2,x3'])

>>> f([2,3,0])
class=Point name=Unnamed dimension=1 values=[5]
But this only works to return a single value as only the last _expression_ is returned,

Otherwise there's an api call to return all values at the same time instead of a single value:
muParserBase.h:107:     value_type  Eval() const;
muParserBase.h:108:    value_type* Eval(int &nStackSize) const;

j


De : users-boun...@openturns.org <users-boun...@openturns.org> de la part de BAUDIN Michael <michael.bau...@edf.fr>

Envoyé : mercredi 14 février 2018 12:30:54
À : users@openturns.org
Objet : [ot-users] Simplified symbolic functions
 

Hi,

 

I have a symbolic function that I would like to simplify and I do not see how.

 

Here is the test case. The function has 8 inputs and 2 outputs. In Python it is simple to define :

 

def functionCrue(X) :

    Q, Ks, Zv, Zm, Hd, Zb, L, B = X

    alpha = (Zm - Zv)/L

    H = (Q/(Ks*B*sqrt(alpha)))**(3.0/5.0)

    Zc = H + Zv

    Zd = Zb + Hd

    S = Zc - Zd

    return [H,S]

myFunction = PythonFunction(8, 2, functionCrue)

 

As you can see, the code is simplified by intermediate variables which are used by subsequent Python statements. For exemple, the slope of the river alpha is first computed, then the height H is computed depending on the slope. Then the variable S is computed based on Zc and Zd, where Zc is computed depending on the height H.

 

When I define the function as a symbolic function, the current definition is more involved.

 

inputs = ['Q', 'Ks', 'Zv', 'Zm', 'Hd', 'Zb', 'L', 'B']

formulas = ['(Q/(Ks*B*sqrt((Zm - Zv)/L)))^(3.0/5.0)','(Q/(Ks*B*sqrt((Zm - Zv)/L)))^(3.0/5.0)+Zv-(Zb + Hd)']

myFunction = SymbolicFunction(inputs, formulas)

 

As you can see, I cannot reuse the value of the first output into the second output.

 

The following interface would be much easier to use. The formulas variable is a list of couples, where the first item is the name of the output variable and the second item is the string to evaluate it.

 

inputs = ['Q', 'Ks', 'Zv', 'Zm', 'Hd', 'Zb', 'L', 'B']

output1 = [‘alpha’, '(Zm - Zv)/L']

output2 = [‘H’, '(Q/(Ks*B*sqrt(alpha)))^(3.0/5.0)']

output3 = [‘Zc’, 'H + Zv']

output4 = [‘Zd’, 'Zb + Hd']

output5 = [‘S’, 'Zc - Zd']

formulas = [output1,output2,output3,output4,output5]

myFunction = SymbolicFunction(inputs, formulas)

 

Is there another way of doing this ? Do you agree that the suggestion is worth being developed ?

 

Best regards,

 

Michaël


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