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## Substitue a variable by a value (Maple and Mupad compatibility) : subs

In Maple and in Mupad, one would use the subs command to substitue a variable by a value in an expression. But the order of the arguments differ between Maple and Mupad. Therefore, to achieve compatibility, Xcas subs command arguments order depends on the mode
• In Maple mode, subs takes two arguments : an equality (variable=substitution value) and the expression.
To substitue several variables in an expression, use a list of equality (variable names = substitution value) as first argument.
• In Mupad or Xcas or TI, subs takes two or three arguments : an expression and an equality (variable=substitution value) or an expression, a variable name and the substitution value.
To substitue several variables, subs takes two ou three arguments :
• an expression of variables and a list of (variable names = substitution value),
• an expression of variables, a list of variables and a list of their substitution values.
subs returns the expression with the substitution done. Note that subs does not quote it's argument, hence in a normal evaluation process, the substitution variable should be purged otherwise it will be replaced by it's assigned value before substitution is done.
Input in Maple mode (if the variable a is purged else input purge(a)) :
subs(a=2,a`^`2+1)
Output
2`^`2+1
Input in Maple mode (if the variables a and b are purged else input purge(a,b)):
subs([a=2,b=1],a`^`2+b)
Output :
2`^`2+1
Input :
subs(a`^`2+1,a=2)
or :
subs(a`^`2+1,a,2)
Output (if the variable a is purged else input purge(a)) :
5
Input :
subs(a`^`2+b,[a=2,b=1])
or :
subs(a`^`2+b,[a,b],[2,1])
Output (if the variables a and b are purged else input purge(a,b)) :
2`^`2+1

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giac documentation written by Renée De Graeve and Bernard Parisse