21.04.2015 Views

The Computable Differential Equation Lecture ... - Bruce E. Shapiro

The Computable Differential Equation Lecture ... - Bruce E. Shapiro

The Computable Differential Equation Lecture ... - Bruce E. Shapiro

SHOW MORE
SHOW LESS

You also want an ePaper? Increase the reach of your titles

YUMPU automatically turns print PDFs into web optimized ePapers that Google loves.

12 CHAPTER 1. CLASSIFYING THE PROBLEM<br />

Solution. As before we obtain<br />

y = cos t + b sin t (1.64)<br />

from the first boundary condition. But now the second condition gives<br />

hence there is precisely one solution:<br />

1 = cos 2 + b sin 2 (1.65)<br />

b = 1 − cos 2 ≈ 1.55741<br />

sin 2<br />

(1.66)<br />

y = cos t + 1 − cos 2<br />

sin 2<br />

sin t (1.67)<br />

Thus we see that the solution of a BVP is not only not necessarily unique, but<br />

there may be an infinite number of solutions. To understand why that is the case<br />

requires delving into the theory of orthogonal functions and generalized Fourier<br />

analysis, which are subjects for other classes. Boundary value problems are also<br />

closely related to partial differential equations.<br />

1.5 <strong>Differential</strong>-Algebraic <strong>Equation</strong>s<br />

Definition 1.7 (<strong>Differential</strong>-Algebraic <strong>Equation</strong>s). Let Let D ∈ R 2n+1 be a set and<br />

suppose that F (t, y, y ′ ) : D ↦→ R n . <strong>The</strong>n<br />

F (t, y, y ′ ) = 0 (1.68)<br />

where the Jacobian matrix ∂ y ′F is singular<br />

∣ det<br />

∂(F 1 , F 2 , . . . ) ∣∣∣<br />

∣ ∂(y 1 ′ , y′ 2 . . . ) = 0 (1.69)<br />

is called an explicit differential-algebraic equation (DAE). If there are some<br />

functions f(t, y, z) and g(t, y, z) and a set of additional algebraic variables z 1 (t), z 2 (t), . . .<br />

such that equation 1.68 can be rewritten as<br />

then the systems is called a semi-explicit DAE.<br />

y ′ = f(t, y, z) (1.70)<br />

0 = g(t, y, z) (1.71)<br />

It is always ( possible to rewrite equation 1.70 as a fully explicit DAE in terms of<br />

y<br />

the vector u = , where z are the algebraic constraints, specifically,<br />

z)<br />

( )<br />

f(t, y, z) − y<br />

′<br />

F (t, y, z) =<br />

g(t, y, z)<br />

(1.72)<br />

Math 582B, Spring 2007<br />

California State University Northridge<br />

c○2007, B.E.<strong>Shapiro</strong><br />

Last revised: May 23, 2007

Hooray! Your file is uploaded and ready to be published.

Saved successfully!

Ooh no, something went wrong!