Chapter 9: Vector Calculus
Section 9.7: Conservative and Solenoidal Fields
Example 9.7.3
Find a scalar potential for F=2 x y−y3 i+x2−3 x y2 j.
Solution
Mathematical Solution
To implement Recipe 1, Table 9.7.4, form and evaluate the following integrals.
∫ax2 b t−b3 dt+∫byx2−3 t2⁢x dt=a⁢b3−x⁢y3−a2⁢b+x2⁢y
The constants a and b can be taken as zero, so the simplest scalar potential for F is then x yx−y2.
Maple Solution - Interactive
Table 9.7.3(a) obtains a scalar potential for F by accessing the ScalarPotential command via the Context Panel.
Initialize
Tools≻Load Package: Student Vector Calculus
Loading Student:-VectorCalculus
Tools≻Tasks≻Browse: Calculus - Vector≻ Vector Algebra and Settings≻ Display Format for Vectors
Press the Access Settings button and select "Display as Column Vector"
Display Format for Vectors
Define the vector field F
Enter the components of F in a free vector. Context Panel: Evaluate and Display Inline
Context Panel: Student Vector Calculus≻Conversions≻To Vector Field
Context Panel: Assign to a Name≻F
2 x y−y3,x2−3 x y2 = →to Vector Field →assign to a nameF
Obtain Maple's scalar potential
Write the name F. Context Panel: Evaluate and Display Inline
Context Panel: Student Vector Calculus≻Scalar Potential
F = →scalar potential−x⁢y3+x2⁢y
Table 9.7.3(a) Context Panel access to the ScalarPotential command
Table 9.7.3(b) implements Recipe 1, Table 9.7.4, and verifies that the result is consistent with the scalar potential found by Maple's ScalarPotential command.
Define the components of F as the functions fx,y and gx,y
Context Panel: Assign Function
fx,y=F1→assign as functionf
gx,y=F2→assign as functiong
Implement Recipe 1, Table 9.7.4
Calculus palette: Definite-integral operator Press the Enter key.
Context Panel: Simplify≻Simplify
Context Panel: Evaluate at a Point≻a=b=0 (See the figure to the right.)
∫axft,b ⅆt+∫bygx,t ⅆt
−b3⁢x−a+b⁢−a2+x2−x⁢−b3+y3+x2⁢y−b
= simplify
a⁢b3−x⁢y3−a2⁢b+x2⁢y
→evaluate at point
−x⁢y3+x2⁢y
Table 9.7.3(b) Implementation of Recipe 1, Table 9.7.4
Maple Solution - Coded
Table 9.7.3(c) obtains the requisite scalar potential via the ScalarPotential command.
Install the Student VectorCalculus package.
withStudent:-VectorCalculus:
Set display of vectors via BasisFormat.
BasisFormatfalse:
Define the vector field F and obtain a scalar potential for it
Define F via the VectorField command.
F≔VectorField2 x y−y3,x2−3 x y2:
Apply the ScalarPotential command.
ScalarPotentialF = −x⁢y3+x2⁢y
Table 9.7.3(c) Application of the ScalarPotential command
Table 9.7.3(d) applies Recipe 1, Table 9.7.4, to obtain the requisite scalar potential.
Define the components of F as the functions f and g
f≔x,y→2 x y−y3:
g≔x,y→x2−3 x y2:
Use the Int command to write the integrals of Recipe 1, Table 9.7.4
Intft,b,t=a..x+Intgx,t,t=b..y
∫ax−b3+2⁢b⁢tⅆt+∫by−3⁢t2⁢x+x2ⅆt
Access the top-level int command by prefixing "colon-dash" to int
u≔:-intft,b,t=a..x+:-intgx,t,t=b..y
Apply the simplify command to the result obtained by use of the eval command for setting a=b=0.
simplifyevalu,a=0,b=0
Table 9.7.3(d) Implementation of Recipe 1, Table 9.7.4
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