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Unformatted text preview: 642:527 SOLUTIONS: ASSIGNMENT 10 FALL 2009 Section 17.7:1. In all sections of this problem the equation is y + y = 0; comparing with the standard SturmLiouville form (1.a) we see that p ( x ) = 1, q ( x ) = 0, and w ( x ) = 1. The solutions of the differential equation are (I) y ( x ) = A cos x + B sin x, if = 2 &gt; , (II) y ( x ) = A + Bx, if = 0 , (III) y ( x ) = A cosh x + B sinh x, if = 2 &lt; , (a) This is just the derivation of the QRS series as a SturmLiouville problem. (c) Similarly, this is the derivation of the QRC series as a SturmLiouville problem. (c) This is the derivation of the HRC series as a SturmLiouville problem. (d) Here the boundary conditions are y (0) = 0, y ( L )+ y ( L ) = 0, i.e., = 0, = = = 1. We analyze the possibilities (I)(III): (I) If y ( x ) = A cos x + B sin x then y (0) = 0 implies that B = 0; then y ( L ) + y ( L ) = 0 implies that A (cos L sin L ) = 0. Since we do not want A = 0 (which leads to a trivial solution) we must have cos L sin L = 0, that is, = cot L . To solve this equation graphically we let u = L , which means that we should solve u/L = cot u . A graphical solution is indicated in Figure 10.1 (the graph is drawn with L = 2, but would look much the same with any value of L ); we see that there is an infinite sequence 0 &lt; u &lt; u 1 &lt; u 2 of solutions. Correspondingly we have solutions n = u n /L of = tan L and eigenvalues n = 2 n . It is clear from the figure that u n n for large n , so that then n ( n/L ) 2 . u u u 1 u 2 u 3 u 4 u 5 u 6 1 2 p 3 2 p 5 2 p 7 2 p 9 2 p 11 2 p y K 2 2 4 6 8 10 Figure 10.1 (II) If y ( x ) = A + Bx then y (0) = 0 implies that B = 0, and then y ( L )+ y ( L ) = 0 implies that A = 0. Only the zero solution exists so = 0 is not an eigenvalue.= 0 is not an eigenvalue....
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This note was uploaded on 12/15/2009 for the course MATH 527 taught by Professor Staff during the Fall '08 term at Rutgers.
 Fall '08
 Staff
 Math

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