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Error, (in simplify/do) invalid simplification command

 Description The simplify command is used to apply simplification rules to an expression.   The Error, (in simplify/do) invalid simplification command message occurs when arguments passed to simplify do not comply with a valid calling sequence.

Examples

Example 1

In this instance, the arguments do not match any of the valid calling sequences of simplify.

 > $\mathrm{simplify}\left({x}^{2},x=y\right)$

Solution 1:

Enclose the equation $x=y$ in a set.

 > $\mathrm{simplify}\left({x}^{2},\left\{x=y\right\}\right)$
 ${{y}}^{{2}}$ (2.1)

Solution 2:

For a direct substitution, you can also use the eval command.

 > $\mathrm{eval}\left({x}^{2},x=y\right)$
 ${{y}}^{{2}}$ (2.2)

Example 2

Here, $\mathrm{eqn}$ provides a side relation that should be used when simplifying the expression $\mathrm{expr}$. The side relations passed to simplify must be a set or list of equations. For more information on side relations, see simplify/siderels.

 > $\mathrm{eqn}≔\mathrm{sin}{\left(x\right)}^{2}+\mathrm{cos}{\left(x\right)}^{2}=1$
 ${\mathrm{eqn}}{:=}{{\mathrm{sin}}{}\left({x}\right)}^{{2}}{+}{{\mathrm{cos}}{}\left({x}\right)}^{{2}}{=}{1}$ (2.3)
 >
 ${\mathrm{expr}}{:=}{{\mathrm{sin}}{}\left({x}\right)}^{{3}}{-}{11}{}{{\mathrm{sin}}{}\left({x}\right)}^{{2}}{}{\mathrm{cos}}{}\left({x}\right){+}{3}{}{{\mathrm{cos}}{}\left({x}\right)}^{{3}}{-}{\mathrm{sin}}{}\left({x}\right){}{\mathrm{cos}}{}\left({x}\right){+}{2}$ (2.4)
 > $\mathrm{simplify}\left(\mathrm{expr},\mathrm{eqn}\right);$

Solution:
Enclose the equation in a set.

 > $\mathrm{eqn}≔\left\{\mathrm{sin}{\left(x\right)}^{2}+\mathrm{cos}{\left(x\right)}^{2}=1\right\}$
 ${\mathrm{eqn}}{:=}\left\{{{\mathrm{sin}}{}\left({x}\right)}^{{2}}{+}{{\mathrm{cos}}{}\left({x}\right)}^{{2}}{=}{1}\right\}$ (2.5)
 >
 ${\mathrm{expr}}{:=}{{\mathrm{sin}}{}\left({x}\right)}^{{3}}{-}{11}{}{{\mathrm{sin}}{}\left({x}\right)}^{{2}}{}{\mathrm{cos}}{}\left({x}\right){+}{3}{}{{\mathrm{cos}}{}\left({x}\right)}^{{3}}{-}{\mathrm{sin}}{}\left({x}\right){}{\mathrm{cos}}{}\left({x}\right){+}{2}$ (2.6)
 > $\mathrm{simplify}\left(\mathrm{expr},\mathrm{eqn}\right);$
 ${2}{-}{\mathrm{sin}}{}\left({x}\right){}{\mathrm{cos}}{}\left({x}\right){+}{14}{}{{\mathrm{cos}}{}\left({x}\right)}^{{3}}{-}{11}{}{\mathrm{cos}}{}\left({x}\right){+}{\mathrm{sin}}{}\left({x}\right){-}{\mathrm{sin}}{}\left({x}\right){}{{\mathrm{cos}}{}\left({x}\right)}^{{2}}$ (2.7)