Math Flashcards
What is Bernoulli’s equation to solve nonlinear ODES
In the form: y’+p(x)y=g(x)y^a
Y^1-a=u
u’+(1-a)pu=(1-a)g
What are the three responses of a damped spring system and what are the corresponding eigenvalues?
- Critically Damped: real double root
- Underdamped: complex root
- Overdamped: distinct real roots
What is the Euler Cauchy equation?
x^2y’’+axy’+by=0
y=x^m
m^2+(a-1)m+b=0
- Y=cx^m
- Y=(c1+c2lnx)x^m
- Y=x^alpha *[Acos(wlnx)+Bsin(wlnx)]
How do you represent the particular solution portion of a forced oscillation?
r(t)=F_ocos(wt)
What are the five kinds of critical points of a system of equation?
- Proper node (Real Same Sign wjth vectors of x and y axis)
- Improper node (Real Same Sign)
- Saddle point (real opposite sign)
- Center (pure imaginary)
5 spiral point (complex)
What are the stability rules for a system of equations?
- Stable and attractive: both negative and non zero
- Stable: both negative or 0
- Unstable: either positive
What are the steps of finding a nonhomogenous solution for a system of equations?
- Solve homogenous solution. Obtain Y(t)c
- Use that Y(t) within u’(t)=Y^-1g (g is the nonhomogenous portion of the result)
- Find Y^-1 and multiply by g
- Take the integral of u’(t)
5 multiple Y(t) by u(t) and add it to the homogenous solution.
What is the generic power series(do not include the series symbol)?
A_m(x-x_0)^m
What is the Fourier power series for
- e^x
- 1/1-x
- cos(x)
- Sin(x)
- X^m/m!
- x^m
- (-1)^m(x^2m)/(2m!)
- (-1)^m(x^2m+1)/(2m+1!)
What is the integral for Laplace Transforms?
L(f)=integral from 0 to inf (e^-st)*f(t)dt
What is the relationship for s shifting?
L[e^at*f(t)]=F(s-a)
What is the relationship for taking the Laplace transform of an integral?
L{integral from 0 to t f(Tau)dTau=F(s)/s
Explain what a unit step function is and how the laplace transform look.
Apply it next to a function to ‘activate’ that function at the given time a. Applying it with a minus sign with ‘deactivate’ that function.
L{u(t-a)}=(e^-as)/s
What is the t-shifting laplace transform?
L{f(t-a)u(t-a)}=(e^-as)*F(s)
-or-
L{f(t)u(t-a)}=(e^-as)L{f(t-a)}
What is the laplace transform for a short impulse?
L{delta(t-a)}=e^-as
How do you use convolution?
Given L(fg)=H(s)
h(t)=(fg)(t)=integral from 0 to t f(Tau)g(t-Tau)dTau
How to use the Variation of Parameters to solve a second order nonhomogenous ODE
Find homogenous solutions and use generic solutions as y1 and y2
yp(x)=-y1integral((y2r)/W)+y2integral((y1r)/W)
W=y1y2’-y1’y2
What is the inverse of a 3x3 matrix
[ c11 -c21 c31
1/det(A) * |-c12 c22 -c32|
[c13 -c23 c33]
What distinguishes a 1. Symmetric Matrix 2. Skew-Symmetric Matrix 3. Orthogonal Matrix
- A=A^T (Real Eigenvalues)
- A=-A^T (Pure Imaginary or Zero Eigvenvalues)
- A^-1=A^T (Pure Imaginary or Zero Eigvenvalues)
What is a diagonalized matrix?
A^^=P^-1AP
A^^=[Eigen1 0;0 Eigven2]
P=[v1 v2];
D^M=x^-1A^MX
What is the inner product? Include the angular relationship between the two vectors.
a*b=a1b1+a2b2+a3b3
cos(gamma)=a*b/|a||b|
What is an example of an inner product?
Wrok done by a force W=p*d
What is the equation for a projection of Vector A in the direction of Vector B?
P=a*b/|b|
What is the Vector product? Include the angular relationship between the two vectors.
Take the cross product of vector A and B
sin(gamma)=|axb|/|a||b|
What are examples of cross product use?
Moment of a force. M=rxp
What is the sclar triple product?
a*(bxc)
What are the parametric representations of
- Circle
- Ellipse
- Straight Line
- Circular Helix
- r(t)=[acost,asint,0]
- r(t)=[acost,bsint,0]
- r(t)=[a1+b1t,a2+b2t,a3+tb3]
- r(t)=[acost,bcost,ct]
What is the equation for the length of a curve?
l=integral from a to b of (sqrt(r’*r’)dt)
What is the equation for arc length?
s(t)= integral from a to t of (sqrt(r’*r’)dt)
What is the equation for the tangent of a curve?
q(w)=r+r’(w)
What is the equation for the curvature of a line?
K(s)=|u’(s)|=|r’‘(s)|
What is the equation for the torsion of a line?
Tau(s)=|b’(s)| where b(s)=u x u’/K
What is the definition of the gradient?
Rate of change of a scalar field f(x,y,z) in a given direction in space. It points in the direction of maximum increase of f
What is the equation of the gradient
grad(f)=[df/dx,df/dy,df/dz]
What is the equation for the directional derivative?
D_bf=b/|b| *grad(f) where b is the direction
What is the Laplace Operator?
Triangle or Upside Triangle Square = [d^2/dx^2,d^2/dy^2,d^2/dz^2]
div(gradf)
What is the divergence?
How much flow is expanding/contracting at a given point?
What is the equation for the divergence?
div V= v1/dx+dv2/dy+dv3/dz
What does it mean to be incompressible?
div V=0
What is the curl of a vector?
The tendency of a vector to rotate about a given point
What is the equation for the curl?
The cross product of the Differential Operator and v
What does it mean to be rotational/irrotational?
Irroational: curl f=0
How do you check if a function is conservative or not?
Nonconservative: curl F ~=0
Conservative: Find the potential function such that grad f=F
What is the equation for a line integral?
int of c (F(r)dr)= int from a to b(F(r(t))r’(t) dt)
How can you check for path independence/exactness?
- Find F=grad(f)
2. curl F=0
How can you simplify the calculation of a line integral if you know it is path independent?
First from F(t) find f(t)
int from a to b(F[r(t)]*r’(t))= f(B)-f(A)
What is the transition from cartesian to radial coordinates for a double integral?
int int f(x,y) dx dy= int int f(rcos(theta),rsin(theta))r dr dtheta
What does Green’s Theorem accomplish?
It provides a transformation between a double integral and a line integral
What is the equation for Green’s Theorem?
int int (dF2/dx-dF1/dy) dx dy= int F*dr
What is the equation for finding the area of an enclosed line?
A=1/2 int xdy-ydx
What is the parametric representation of a
- Cylinder
- Sphere
- Cone
- r(u,v)=[acosu,asinu,v]
- r(u,v)=[acosucosv,asinucosv,sinv]
- r(u,v)=[ucosv,usinv,u]
Find the unit normal vector given representation g(x,y,z)
n=grad(g)/|grad(g)|
What is the equation for a surface integral?
int int F_n Da= int int F(r(u,v))*N(u,v) du dv
where N(u,v)=r_u x r_v
What is the equation for the area of a surface?
A(s)=int int |r_u x r_v| du dv
What does the Divergence Theorem of Gauss do?
Provides a transformation between triple integrals and surface integrals
What is the Divergence Theorem of Gauss Eq?
int int int div(F) dV= int int F*n dA
What does Stoke’s Theorem accomplish?
It provides a transformation between surface and line integral