For i,2,ñ © Loop to find higher-order derivatives
(e,x)+e1*(e,y)→e
EndFor
e © Return derivative.
© (Replace with factor(e) to automatically factor result.)
EndFunc
The arguments are
impdifn(expression, independent variable, dependent variable, order)
expression may be an algebraic expression, or an equation. order is the order of the derivative: 1 for
the first derivative, 2 for the second and so on.
For example, the call to find the second derivative of x^4 + y^4 = 0 is
impdifn(x^4+y^4,x,y,2)
which returns
−3$x
6
y
7
−
3$x
2
y
3
You can apply factor() to this expression to get
−3$x
2
$
x
4
+y
4
y
7
which is zero, since x^4 + y^4 = 0.
Don Phillips modified David Stoutemyer's impdifn() to handle equations as input arguments, and
automatically factor the result. I modified Don's routine by removing the automatic factoring of the
result (you can do this manually, when needed), and converting a Loop ... EndLoop to a For loop.
If you use the first, manual method to find the derivative of an equation, this warning may be shown in
the status line: Warning: Differentiating an equation may produce a false equation.
(Credit to Bhuvanesh Bhatt and Kevin Kofler)
[6.54] Delete variables after using numeric solver
The variables in the numeric solver exist in the current folder after exiting the solver, which can be
useful if you run the solver again with the same equation. Since the variables do take up memory and
may interfere with further calculations, this tip shows a convenient method to delete them.
The current solver equation is stored in the system variable eqn. We can use the RCL feature to recall
eqn without variable substitution, so we can see the variables. Then, the functions delvar1() and
exprvars() can automatically extract and delete the variables. exprvars() returns the eqn variables as a
list with string elements, and delvar1() deletes a list of variables. Assuming that delvar1() and
exprvars() are both stored in the util\ folder, enter this:
util\delvar1(util\exprvars("
Next press [RCL] to display the Recall Variable dialog box. [RCL] is [2nd] [STO] on both calculators.
Type [e] [q] [n] [ENTER] [ENTER] to recall the eqn system variable, then type ["] [ ) ] [ ) ] [ENTER]. The
variables are then deleted.
6 - 92
To Next Page
Loading...
Need help?
General
