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# For example evaluate the solution at u 1 and t 1 eval

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Unformatted text preview: , {1 = 1, 3 = 3}] This method can be valuable if your equation has many solutions, or if you are unsure of the number of solutions that a certain command produces. Restricting Solutions You can limit solutions by specifying inequalities with the solve command. &gt; solve({x^2=y^2},{x,y}); 48 • Chapter 3: Finding Solutions {x = −y, y = y }, {y = y, x = y } &gt; solve({x^2=y^2, x&lt;&gt;y},{x,y}); {x = −y, y = y } Consider this system of ﬁve equations in ﬁve unknowns. &gt; &gt; &gt; &gt; &gt; eqn1 eqn2 eqn3 eqn4 eqn5 := := := := := x+2*y+3*z+4*t+5*u=41: 5*x+5*y+4*z+3*t+2*u=20: 3*y+4*z-8*t+2*u=125: x+y+z+t+u=9: 8*x+4*z+3*t+2*u=11: Solve the system for all variables. &gt; s1 := solve({eqn1,eqn2,eqn3,eqn4,eqn5}, {x,y,z,t,u}); s1 := {x = 2, t = −11, z = −1, y = 3, u = 16} Solving for a Subset of Unknowns You can also solve for a subset of the unknowns. Maple returns the solutions in terms of the other unknowns. &gt; s2 := solve({eqn1,eqn2,eqn3}, { x, y, z}); 527 28 70 59 − 7t − u, z = − − 7 t − u, 13 13 13 13 70 635 + 12 t + u} y= 13 13 s2 := {x = − Exploring Solutions You can explore the parametric solutions found at the end of the previous section. For example, evaluate the solution at u = 1 and t = 1. &gt; eval( s2, {u=1,t=1} ); {x = 861 −220 −646 ,y= ,z= } 13 13 13 Suppose that you require the solutions from solve in a particular order. Since you cannot ﬁx the order of elements in a set, solve does not necessarily return your solutions in the order x, y, z . However, lists do preserve order. Try the following. 3.1 The Maple solve Command &gt; eval( [x,y,z], s2 ); • 49 [− 28 635 70 70 59 527 − 7t − u, + 12 t + u, − − 7 t − u] 13 13 13 13 13 13 This command ﬁxed the order and extracted the right-hand side of the equations. Because the order is ﬁxed, you know the solution for each variable. This capability is particularly useful if you want to plot the solution surface. &gt; plot3d(%, u=0..2, t=0..2, axes=BOXED); –5 –10 –15 –20 –25 50 55 60 65 –58 –56 –54 –52 –50 –48 –46 –44 –42 70 75 80 The unapply Command For convenience, deﬁne x = x(u, t), y = y (u, t), and z = z (u, t), that is, convert the solutions to functions. Recall that you can easily select a solution expression for a particular variable using eval. &gt; eval( x, s2 ); − 527 28 − 7t − u 13 13 However, this is an expression for x and not a function. &gt; x(1,1); x(1, 1) To convert the expression to a function, use the unapply command. Provide unapply with the expression and the independent variables. For example, 50 • Chapter 3: Finding Solutions &gt; f := unapply(x^2 + y^2 + 4, x, y); f := (x, y ) → x2 + y 2 + 4 produces the function, f , of x and y that maps (x, y ) to x2 + y 2 + 4. This new function is easy to use. &gt; f(a,b); a2 + b2 + 4 Thus, to make your solution for x a function of both u and t, obtain the expression for x, as above. &gt; eval(x, s2); − 28 527 − 7t − u 13 13 Use unapply to turn it into a function of u and t. &gt; x := unapply(%, u, t); x := (u, t...
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