# Sample program written in rnpl as a language guide
# This program solves 1D 2nd order wave equation
# phi_tt = phi_xx (string with endpoints fixed)
# Phi=phi_x  Pi=phi_t

# This is how to set the memory size
system parameter int memsiz := 1000000

parameter float xmin := 0
parameter float xmax := 100
parameter float amp := 1.0
parameter float cent
parameter float sigma

rect coordinates t,x

uniform rect grid g1 [1:Nx] {xmin:xmax}
#uniform rect grid g1 

float phi on g1 at -1,0,1

attribute int out_gf encodeone := [1 0]

operator D_LF(f,x,x) := (<0>f[1] - 2*<0>f[0] + <0>f[-1])/(dx*dx)
operator D_LF(f,t,t) := (<1>f[0] - 2*<0>f[0] + <-1>f[0])/(dt*dt)
operator D_LF(f,t) := (<1>f[0] - <-1>f[0])/(2*dt)

evaluate residual phi { [1:1] := D_LF(phi,t);
            [2:Nx-1] := D_LF(phi,t,t) - D_LF(phi,x,x);
             [Nx:Nx] := D_LF(phi,t) }

#evaluate residual phi { [0:0] := D_LF(phi,t);
#            [1:Nx-2] := D_LF(phi,t,t) - D_LF(phi,x,x);
#         [Nx-1:Nx-1] := D_LF(phi,t) }

initialize phi {[1:Nx] := amp*exp(-(x-cent)^2/sigma^2)}

looper iterative

auto update phi

##Save from here to end of file to separate file (w1d_0), edit and remove 
##first '#' from every line.
##
##parameters for wave1d
#tag := "1d_"
#lambda := .8
#Nx0 := 100
#level := 0
#xmin := 0
#xmax := 10
#ser := 0
#fout := 1
#iter := 1000
#epsiter := 1.0e-5
#rmod := 10
#amp := 1.0
#cent := 5.0
#sigma := 0.8
#in_file := "w_in.sdf"
#out_file := "w_out.sdf"