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Merge pull request #14 from acroy/api-yout
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RFC: Duck typing and consistent return types for all solvers.
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@ivarne
ivarne committed Mar 12, 2014
2 parents 817c6e6 + 5686490 commit 421e370
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158 changes: 88 additions & 70 deletions src/ODE.jl
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Original file line number Diff line number Diff line change
Expand Up @@ -43,8 +43,7 @@ export ode23, ode4, ode45, ode4s, ode4ms
# Initialize variables.
# Adapted from Cleve Moler's textbook
# http://www.mathworks.com/moler/ncm/ode23tx.m
function ode23{T}(F::Function, tspan::AbstractVector, y0::AbstractVector{T}; reltol = 1.e-5, abstol = 1.e-8)

function ode23(F, y0, tspan; reltol = 1.e-5, abstol = 1.e-8)
if reltol == 0
warn("setting reltol = 0 gives a step size of zero")
end
Expand All @@ -58,7 +57,8 @@ function ode23{T}(F::Function, tspan::AbstractVector, y0::AbstractVector{T}; rel
y = y0

tout = t
yout = y.'
yout = Array(typeof(y0),1)
yout[1] = y

tlen = length(t)

Expand Down Expand Up @@ -101,7 +101,7 @@ function ode23{T}(F::Function, tspan::AbstractVector, y0::AbstractVector{T}; rel
t = tnew
y = ynew
tout = [tout; t]
yout = [yout; y.']
push!(yout, y)
s1 = s4 # Reuse final function value to start new step
end

Expand All @@ -118,11 +118,12 @@ function ode23{T}(F::Function, tspan::AbstractVector, y0::AbstractVector{T}; rel

end # while (t != tfinal)

return (tout, yout)
return tout, yout

end # ode23



# ode45 adapted from http://users.powernet.co.uk/kienzle/octave/matcompat/scripts/ode_v1.11/ode45.m
# (a newer version (v1.15) can be found here https://sites.google.com/site/comperem/home/ode_solvers)
#
Expand Down Expand Up @@ -180,9 +181,7 @@ end # ode23
# [email protected]
# created : 06 October 1999
# modified: 17 January 2001

function oderkf{T}(F::Function, tspan::AbstractVector, x0::AbstractVector{T}, a, b4, b5; reltol = 1.0e-5, abstol = 1.0e-8)

function oderkf(F, x0, tspan, a, b4, b5; reltol = 1.0e-5, abstol = 1.0e-8)
# see p.91 in the Ascher & Petzold reference for more infomation.
pow = 1/5

Expand All @@ -196,25 +195,26 @@ function oderkf{T}(F::Function, tspan::AbstractVector, x0::AbstractVector{T}, a,
h = (tfinal - t)/100 # initial guess at a step size
x = x0
tout = t # first output time
xout = x.' # first output solution
xout = Array(typeof(x0), 1)
xout[1] = x # first output solution

k = zeros(eltype(x), length(c), length(x))
k[1,:] = F(t,x) # first stage
k = Array(typeof(x0), length(c))
k[1] = F(t,x) # first stage

while t < tfinal && h >= hmin
if t + h > tfinal
h = tfinal - t
end

for j = 2:length(c)
k[j,:] = F(t + h.*c[j], x + h.*(a[j,1:j-1]*k[1:j-1,:]).')
k[j] = F(t + h.*c[j], x + h.*(a[j,1:j-1]*k[1:j-1])[1])
end

# compute the 4th order estimate
x4 = x + h.*(b4*k).'
x4 = x + h.*(b4*k)[1]

# compute the 5th order estimate
x5 = x + h.*(b5*k).'
x5 = x + h.*(b5*k)[1]

# estimate the local truncation error
gamma1 = x5 - x4
Expand All @@ -228,7 +228,7 @@ function oderkf{T}(F::Function, tspan::AbstractVector, x0::AbstractVector{T}, a,
t = t + h
x = x5 # <-- using the higher order estimate is called 'local extrapolation'
tout = [tout; t]
xout = [xout; x.']
push!(xout, x)

# Compute the slopes by computing the k[:,j+1]'th column based on the previous k[:,1:j] columns
# notes: k needs to end up as an Nxs, a is 7x6, which is s by (s-1),
Expand All @@ -238,9 +238,9 @@ function oderkf{T}(F::Function, tspan::AbstractVector, x0::AbstractVector{T}, a,
# This is part of the Dormand-Prince pair caveat.
# k[:,7] has already been computed, so use it instead of recomputing it
# again as k[:,1] during the next step.
k[1,:] = k[end,:]
k[1] = k[end]
else
k[1,:] = F(t,x) # first stage
k[1] = F(t,x) # first stage
end
end

Expand All @@ -252,7 +252,7 @@ function oderkf{T}(F::Function, tspan::AbstractVector, x0::AbstractVector{T}, a,
println("Step size grew too small. t=", t, ", h=", h, ", x=", x)
end

return (tout, xout)
return tout, xout
end

# Both the Dormand-Prince and Fehlberg 4(5) coefficients are from a tableau in
Expand All @@ -273,7 +273,7 @@ const dp_coefficients = ([ 0 0 0 0 0
# 5th order b-coefficients
[35/384 0 500/1113 125/192 -2187/6784 11/84 0],
)
ode45_dp(F, tspan, x0; kwargs...) = oderkf(F, tspan, x0, dp_coefficients...; kwargs...)
ode45_dp(F, x0, tspan; kwargs...) = oderkf(F, x0, tspan, dp_coefficients...; kwargs...)

# Fehlberg coefficients
const fb_coefficients = ([ 0 0 0 0 0
Expand All @@ -287,7 +287,7 @@ const fb_coefficients = ([ 0 0 0 0 0
# 5th order b-coefficients
[16/135 0 6656/12825 28561/56430 -9/50 2/55],
)
ode45_fb(F, tspan, x0; kwargs...) = oderkf(F, tspan, x0, fb_coefficients...; kwargs...)
ode45_fb(F, x0, tspan; kwargs...) = oderkf(F, x0, tspan, fb_coefficients...; kwargs...)

# Cash-Karp coefficients
# Numerical Recipes in Fortran 77
Expand All @@ -302,7 +302,7 @@ const ck_coefficients = ([ 0 0 0 0 0
# 5th order b-coefficients
[2825/27648 0 18575/48384 13525/55296 277/14336 1/4],
)
ode45_ck(F, tspan, x0; kwargs...) = oderkf(F, tspan, x0, ck_coefficients...; kwargs...)
ode45_ck(F, x0, tspan; kwargs...) = oderkf(F, x0, tspan, ck_coefficients...; kwargs...)

# Use Dormand Prince version of ode45 by default
const ode45 = ode45_dp
Expand All @@ -316,67 +316,87 @@ const ode45 = ode45_dp
# ODEFUN(T,X) must return a column vector corresponding to f(t,x). Each
# row in the solution array X corresponds to a time returned in the
# column vector T.
function ode4{T}(F::Function, tspan::AbstractVector, x0::AbstractVector{T})
function ode4(F, x0, tspan)
h = diff(tspan)
x = Array(T, length(tspan), length(x0))
x[1,:] = x0
x = Array(typeof(x0), length(tspan))
x[1] = x0

midxdot = Array(T, 4, length(x0))
midxdot = Array(typeof(x0), 4)
for i = 1:length(tspan)-1
# Compute midstep derivatives
midxdot[1,:] = F(tspan[i], x[i,:]')
midxdot[2,:] = F(tspan[i]+h[i]./2, x[i,:]' + midxdot[1,:]'.*h[i]./2)
midxdot[3,:] = F(tspan[i]+h[i]./2, x[i,:]' + midxdot[2,:]'.*h[i]./2)
midxdot[4,:] = F(tspan[i]+h[i], x[i,:]' + midxdot[3,:]'.*h[i])
midxdot[1] = F(tspan[i], x[i])
midxdot[2] = 2*F(tspan[i]+h[i]./2, x[i] + midxdot[1].*h[i]./2)
midxdot[3] = 2*F(tspan[i]+h[i]./2, x[i] + midxdot[2].*h[i]./2)
midxdot[4] = F(tspan[i]+h[i], x[i] + midxdot[3].*h[i])

# Integrate
x[i+1,:] = x[i,:] + 1./6.*h[i].*[1 2 2 1]*midxdot
x[i+1] = x[i] + 1/6 .*h[i].*sum(midxdot)
end
return (tspan, x)
return [tspan], x
end

#ODEROSENBROCK Solve stiff differential equations, Rosenbrock method
# with provided coefficients.
function oderosenbrock{T}(F::Function, G::Function, tspan::AbstractVector, x0::AbstractVector{T}, gamma, a, b, c)
function oderosenbrock(F, x0, tspan, gamma, a, b, c; jacobian=nothing)
# Crude forward finite differences estimator as fallback
# FIXME: This doesn't really work if x is anything but a Vector or a scalar
function fdjacobian(F, x::Number, t)
ftx = F(t, x)

# The 100 below is heuristic
dx = (x .+ (x==0))./100
dFdx = (F(t,x+dx)-ftx)./dx

return dFdx
end

function fdjacobian(F, x, t)
ftx = F(t, x)
lx = max(length(x),1)
dFdx = zeros(eltype(x), lx, lx)
for j = 1:lx
# The 100 below is heuristic
dx = zeros(eltype(x), lx)
dx[j] = (x[j] .+ (x[j]==0))./100
dFdx[:,j] = (F(t,x+dx)-ftx)./dx[j]
end
return dFdx
end

if typeof(jacobian) == Function
G = jacobian
else
G = (t, x)->fdjacobian(F, x, t)
end

h = diff(tspan)
x = Array(T, length(tspan), length(x0))
x[1,:] = x0
x = Array(typeof(x0), length(tspan))
x[1] = x0

solstep = 1
while tspan[solstep] < maximum(tspan)
ts = tspan[solstep]
hs = h[solstep]
xs = reshape(x[solstep,:], size(x0))
xs = x[solstep]
dFdx = G(ts, xs)
jac = eye(size(dFdx,1))./gamma./hs-dFdx
# FIXME
if size(dFdx,1) == 1
jac = 1/gamma/hs - dFdx[1]
else
jac = eye(dFdx)./gamma./hs - dFdx
end

g = zeros(size(a,1), length(x0))
g[1,:] = jac \ F(ts + b[1].*hs, xs)
g = Array(typeof(x0), size(a,1))
g[1] = (jac \ F(ts + b[1].*hs, xs))
for i = 2:size(a,1)
g[i,:] = jac \ (F(ts + b[i].*hs, xs + (a[i,1:i-1]*g[1:i-1,:]).') + (c[i,1:i-1]*g[1:i-1,:]).'./hs)
g[i] = (jac \ (F(ts + b[i].*hs, xs + (a[i,1:i-1]*g[1:i-1])[1]) + (c[i,1:i-1]*g[1:i-1])[1]./hs))
end

x[solstep+1,:] = x[solstep,:] + b*g
x[solstep+1] = x[solstep] + (b*g)[1]
solstep += 1
end
return (tspan, x)
return [tspan], x
end

function oderosenbrock{T}(F::Function, tspan::AbstractVector, x0::AbstractVector{T}, gamma, a, b, c)
# Crude forward finite differences estimator as fallback
function jacobian(F::Function, t::Number, x::AbstractVector)
ftx = F(t, x)
dFdx = zeros(length(x), length(x))
for j = 1:length(x)
dx = zeros(size(x))
# The 100 below is heuristic
dx[j] = (x[j]+(x[j]==0))./100
dFdx[:,j] = (F(t,x+dx)-ftx)./dx[j]
end
return dFdx
end
oderosenbrock(F, (t, x)->jacobian(F, t, x), tspan, x0, gamma, a, b, c)
end

# Kaps-Rentrop coefficients
const kr4_coefficients = (0.231,
Expand All @@ -389,8 +409,9 @@ const kr4_coefficients = (0.231,
-5.07167533877 0 0 0
6.02015272865 0.1597500684673 0 0
-1.856343618677 -8.50538085819 -2.08407513602 0],)
ode4s_kr(F, tspan, x0) = oderosenbrock(F, tspan, x0, kr4_coefficients...)
ode4s_kr(F, G, tspan, x0) = oderosenbrock(F, G, tspan, x0, kr4_coefficients...)

ode4s_kr(F, x0, tspan; jacobian=nothing) = oderosenbrock(F, x0, tspan, kr4_coefficients...; jacobian=jacobian)

# Shampine coefficients
const s4_coefficients = (0.5,
[ 0 0 0 0
Expand All @@ -403,19 +424,16 @@ const s4_coefficients = (0.5,
372/25 12/5 0 0
-112/125 -54/125 -2/5 0],)



ode4s_s(F, tspan, x0) = oderosenbrock(F, tspan, x0, s4_coefficients...)
ode4s_s(F, G, tspan, x0) = oderosenbrock(F, G, tspan, x0, s4_coefficients...)
ode4s_s(F, x0, tspan; jacobian=nothing) = oderosenbrock(F, x0, tspan, s4_coefficients...; jacobian=jacobian)

# Use Shampine coefficients by default (matching Numerical Recipes)
const ode4s = ode4s_s

# ODE_MS Fixed-step, fixed-order multi-step numerical method with Adams-Bashforth-Moulton coefficients
function ode_ms{T}(F::Function, tspan::AbstractVector, x0::AbstractVector{T}, order::Integer)
function ode_ms(F, x0, tspan, order::Integer)
h = diff(tspan)
x = zeros(T, length(tspan), length(x0))
x[1,:] = x0
x = Array(typeof(x0), length(tspan))
x[1] = x0

if 1 <= order <= 4
b = [ 1 0 0 0
Expand All @@ -438,13 +456,13 @@ function ode_ms{T}(F::Function, tspan::AbstractVector, x0::AbstractVector{T}, or
for i = 1:length(tspan)-1
# Need to run the first several steps at reduced order
steporder = min(i, order)
xdot[i,:] = F(tspan[i], x[i,:]')
x[i+1,:] = x[i,:] + b[steporder,1:steporder]*xdot[i-(steporder-1):i,:].*h[i]
xdot[i] = F(tspan[i], x[i])
x[i+1] = x[i] + (b[steporder,1:steporder]*xdot[i-(steporder-1):i])[1].*h[i]
end
return (tspan, x)
return [tspan], x
end

# Use order 4 by default
ode4ms(F, tspan, x0) = ode_ms(F, tspan, x0, 4)
ode4ms(F, x0, tspan) = ode_ms(F, x0, tspan, 4)

end # module ODE
11 changes: 6 additions & 5 deletions test/tests.jl
View file
Original file line number Diff line number Diff line change
Expand Up @@ -19,28 +19,29 @@ for solver in solvers
# dy
# -- = 6 ==> y = 6t
# dt
t,y=solver((t,y)->6, [0:.1:1], [0.])
t,y=solver((t,y)->6, 0., [0:.1:1])
@test maximum(abs(y-6t)) < tol

# dy
# -- = 2t ==> y = t.^2
# dt
t,y=solver((t,y)->2t, [0:.001:1], [0.])
t,y=solver((t,y)->2t, 0., [0:.001:1])
@test maximum(abs(y-t.^2)) < tol

# dy
# -- = y ==> y = y0*e.^t
# dt
t,y=solver((t,y)->y, [0:.001:1], [1.])
t,y=solver((t,y)->y, 1., [0:.001:1])
@test maximum(abs(y-e.^t)) < tol

# dv dw
# -- = -w, -- = v ==> v = v0*cos(t) - w0*sin(t), w = w0*cos(t) + v0*sin(t)
# dt dt
#
# y = [v, w]
t,y=solver((t,y)->[-y[2], y[1]], [0:.001:2*pi], [1., 2.])
@test maximum(abs(y-[cos(t)-2*sin(t) 2*cos(t)+sin(t)])) < tol
t,y=solver((t,y)->[-y[2], y[1]], [1., 2.], [0:.001:2*pi])
ys = hcat(y...).' # convert Vector{Vector{Float}} to Matrix{Float}
@test maximum(abs(ys-[cos(t)-2*sin(t) 2*cos(t)+sin(t)])) < tol
end

println("All looks OK")

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