Octopus arm simulator 

Description:
	Functions for initiating and moving the simulated octopus arm.

Usage:
	initOctarm(...)

	initOctarm( nComp=10, State=initiateArm(),
	            bdefAct=TRUE, baseAct=0, muscAct=array(0,c(length(baseAct),nComp+1,3)),
	            Ta=1320,Tp=200,alpha0=9, kv = 1e-6,
	            rho_arm=1200,rho_water=1025, ga=9.8, 
	            goal=c(-1,-1,0.1), bdraw=FALSE)
	
	moveOctarm(state, action, ...)

	moveOctarm( state, action, dt=0.01, nsteps=1,
	            userActM=matrix(0,NC1,3), userActB=0,
	            draw=1, sleep=0.01)

Arguments:

    nComp           the number of compartment 
    bdefAct         use defined action set, if FALSE need to set below three
        baseAct     base activations ( vector with naction values )
        muscAct     muscle activations (3 dimensional array [action, nComp+1, 3]
                    value for each action element in range of [0,1]
    Ta              the active stiffness
    Tp              the passive stiffness
    alpha0          the linear dampening coefficient
    kv              kinetic velocity
    rho_arm         density for an octopus arm 
    rho_water       density for seawater
    ga              gravitational acceleration
    goal            the position and radius of goal

    state       initial state
    action      predefined action index (>=1)
                0 for user-defined activation
                -1 for random action 
    dt          time interval for each step
    nsteps      the number of steps 
    userActM    user defined muscle activation (action should be set to -2)
    userActB    user defined base activation (action should be set to -2)
    draw        draw the simulation
    sleep       interval between each steps

Return Value:
	State with position and velocity after initiating and moving the arm

Example:

	st <- initOctarm(bdefAct=FALSE) 
	st <- moveOctarm(st, -1, nsteps=1000) 
	st <- moveOctarm(st, 0, nsteps=10000, userActM=matrix(c(1,0,0),NC1,3,byr
	st <- moveOctarm(st, 0, nsteps=10000, userActM=matrix(c(0,1,0),NC1,3,byr

	st <- initOctarm()
	st <- moveOctarm(st, 1, nsteps=1000)