# #Multivariable Calculus Package # # # #
Multivariable Calculus Package

#Maple procs for use in Andrew, Samir, and Charlie's Lab investigating tangent planes
#By Charles McGarraugh with help from Samir Murty and Andrew Youn

#This is the routine for plotting a tangent plane to a graph at a given point

GraphTan := proc(f,xrange,yrange,pt)
#Define local variables
local xmin,xmax,ymin,ymax,x0,y0,z0,dx,dy,xvec,yvec,tanfunc,gpha,gphb,tanpt;
#Allow us to use (display) command
with (plots,pointplot):
with (plots,display):

#Extract the different variables we will need from the larger variables given as input from user 
x0 := op(2,pt)[1]:
y0 := op(2,pt)[2]:
xmin := op(1,op(2,xrange)): 
xmax := op(2,op(2,xrange)): 
ymin := op(1,op(2,yrange)): 
ymax := op(2,op(2,yrange)): 
 
#Define the surface as variable name gpha      
 gpha := plot3d(f,xrange,yrange,style=HIDDEN,axes=BOXED): 

#Evaluate partials with respect to x and y at (x0, y0) 
dx := subs(x=x0,y=y0,diff(f,x)): 
 dy := subs(x=x0,y=y0,diff(f,y)):

#Find  height of function at x0,y0
z0 := subs(x=x0,y=y0,f): 

#Use partials to get tangent vectors 
 xvec := [1,0,dx]:
 yvec := [0,1,dy]:

#Find the parameterized plane of using the tangent vectors as basis and raise it to height z0
    tanfunc := evalm(t*xvec+s*yvec+[x0,y0,z0]): 

#Plot tangent point as tanpt and tangent plane as gphb
    tanpt := pointplot({[x0,y0,z0]},color=black): 
    gphb:=plot3d(tanfunc,t=-(xmax-xmin)/4..(xmax-xmin)/4,s=-(ymax-ymin)/4..(ymax-ymin)/4,style=PATCHNOGRID): 

#Display the surface graph, tangent plane, and tangent point
display ([gpha, gphb,tanpt]);
end:



#This is the routine for plotting a tangent plane to a parametric curve in variables s and t

ParamTan:= proc (f,srange,trange,pt)
#Define local variables
local planefunc,s0,t0,smin,smax,tmin,tmax,pama,dfs,dft,z0,pamb,pamc,tanpt;
#Allow us to use (display) and (pointplot) commands
with(plots,pointplot):
with(plots,display): 

#Extract specific variables we need from the larger variables define as input from user
s0:= op (2,pt)[1]: 
t0:= op (2,pt)[2]: 
smin := op(1,op(2,srange)):  
smax := op(2,op(2,srange)):  
tmin := op(1,op(2,trange)): 
tmax := op(2,op(2,trange)):

#Plot the parametric surface.  Note: f is a 3-vector as defined by user
    pama:= plot3d(f,srange,trange,style=HIDDEN,axes=BOXED):

# Find the tanget vectors by taking partials with respect to s and then to t
    dfs := subs(s=s0,t=t0,diff(f,s)):
    dft := subs(s=s0,t=t0,diff(f,t)):

#Find the point of tangency 
   z0  := subs (s=s0,t=t0,f);

#Plot point of tangency under variable name tanpt    
  tanpt := pointplot ({z0},color=black):

# Parameterize plane using tangent vectors and k,l as parameters, add z0 to give proper translation
   planefunc := evalm (k*dfs+l*dft+z0):

#Plot the tangent plane under variable name pamb, limit parameters so as not to obstruct viewing
   pamb:=plot3d(planefunc,k=-(smax-smin)/8..(smax-smin)/8,l=-(tmax-tmin)/8..(tmax-tmin)/8,style=PATCHNOGRID): 

#Display the plots
display ([pama,pamb,tanpt]);
end: 



#This is the routine to plot the tangent plane to an implicitly defined function

ImplicitTan := proc (F,xrange,yrange,zrange,pt)
#Define local variable names
local f,K,gradat,tanpt,x0,y0,z0,impa,impb,dx,dy,dz,vec0,planefunc;
#Allows us to use (implicitplot3D), (display), and (pointplot) commands
with(plots,pointplot):
with(plots,display):
with(plots,implicitplot3d):

# Allows (innerprod) command
with (linalg,innerprod):

#Extract different variables we need from larger variable given by user input
x0 := op (2,pt)[1]:
y0 := op (2,pt)[2]:
z0 := op (2,pt)[3]:

#Plot implicit surface under variable name impa
impa := implicitplot3d(F,xrange,yrange,zrange,style=HIDDEN,axes=BOXED):

#If F is just an expression rename it f
  f := F:

#If F is an equation, extract the expression as f and the constant as K
if type(F,`=`) = 'true' then
		f:= lhs (F):
		K := rhs (F):	
fi;

#Evaluate partials of f with repect to x, y, and z.
	dx := subs(x=x0,y=y0,z=z0,diff(f,x)):
	dy := subs(x=x0,y=y0,z=z0,diff(f,y)):
	dz := subs(x=x0,y=y0,z=z0,diff(f,z)):
	
#Create the gradient vector at [x0,y0,z0] Which we know is normal to suface
	gradat := [dx,dy,dz]:

#Find the fuction for tangent plane (implicitly defined) 
#Using fact that plane is given by--    grad(x0,y0,z0) dot ([x-x0,y-y0,z-z0]) = 0 

	vec0:=  (evalm([x,y,z]-[x0,y0,z0])):
	planefunc:= innerprod(gradat,vec0):
	
#Plot tangent plane under variable name impb
	impb := implicitplot3d(planefunc,xrange,yrange,zrange):

#Plot point of tangency		
	tanpt := pointplot({[x0,y0,z0]},color=red):

#Display surface, tangent plane, tangent point
display ([impa,impb,tanpt]);
end: