REM nm7bbc.bas - jackord@kw.igs.net - 21 Nov 07 - BBC Basic v5.50b
      REM wave pulse incident on a variable thickness segment where the mass density
      REM   increases by a factor of 1.44 followed by a region where the mass density
      REM   increases again by a factor of 1.44
      REM the motion is generated directly from Newton's Law
      REM   or a superposition of (non-orthogonal) normal mode displacements
      *FLOAT64
      INSTALL @lib$+"WINLIB5"
      
      REM Initialize Window
      b1% = FN_button("Pulse B", 10, 5, 60, 20, FN_setproc(PROCp1), 0)
      b2% = FN_button("Motion", 80, 5, 60, 20, FN_setproc(PROCp2), 0)
      c1% = FN_combobox("", 150, 5, 90, 120, 0, 3)
      c2% = FN_combobox("", 250, 5, 70, 40, 0, 3)
      WindowWidth=480
      WindowHeight=220
      VDU 23,22,WindowWidth;WindowHeight;8,15,16,128
      SYS "SetWindowText", @hwnd%, "Pulse Striking Interface"
      SYS "SendMessage", c1%, &143, 0, "D(film)=0"
      SYS "SendMessage", c1%, &143, 1, "D(film)=5"
      SYS "SendMessage", c1%, &143, 1, "D(film)=10"
      SYS "SendMessage", c1%, &14E, 0, 0
      SYS "SendMessage", c2%, &143, 0, "F=ma"
      SYS "SendMessage", c2%, &143, 1, "FFSS"
      SYS "SendMessage", c2%, &14E, 0, 0
      DIM y(480): DIM v(480)
      n=480: nf=320: nk=4: kk=0: dt=0.9: no=48: nw=96
      OFF: VDU 5
      
      REPEAT
        WAIT 1
      UNTIL FALSE
      QUIT
      
      DEF PROCp1: kk=1: jt=0: plt=0                  : REM Pulse B
      
      DEF PROCp2: IF kk>0 THEN plt=1                 : REM Motion
      
      IF jt=0 THEN
        SYS "SendMessage", c1%, &147, 0, 0 TO ch1%
        SYS "SendMessage", c2%, &147, 0, 0 TO ch2%
        dl=5*ch1%: e1=0: e2=0
        FOR i=0 TO n                                 : REM Initialize
          y(i)=0: v(i)=0
        NEXT i
        FOR i=no TO no+nw
          q=(i-no)*2*PI/nw
          y(i)=80*(1-COS(q))
          v(i)=-80*2*PI/nw*SIN(q)
          v(i)=v(i)*COS(nk*q)+y(i)*nk*2*PI/nw*SIN(nk*q)
          y(i)=y(i)*COS(nk*q)
          e1=e1+v(i)*v(i)
        NEXT i
        FOR i=no TO no+nw                            : REM Feynman half-step
          v(i)=v(i)+(y(i-1)+y(i+1)-2*y(i))*dt/2
        NEXT i
      ENDIF
      IF plt=1 THEN * REFRESH OFF
      tt=TIME
      WHILE jt=0 OR plt=1
        CLS: GCOL 0: MOVE 700, 420: PRINT "Frame "; jt; "/320"
        GCOL 12: MOVE 0, 190
        FOR i=1 TO n
          IF i=n/2 THEN GCOL 10
          IF i=n/2+dl THEN GCOL 9
          DRAW 2*i, 190+INT(y(i)+1)
        NEXT i
        IF plt=1 THEN * REFRESH
        jt=jt+1
        FOR i=1 TO n-1                               : REM F=ma
          y(i)=y(i)+v(i)*dt
        NEXT i
        m=1
        FOR i=1 TO n-1
          IF i=n/2 THEN m=1.44*m
          IF i=n/2+dl THEN m=m*1.44
          v(i)=v(i)+(y(i-1)+y(i+1)-2*y(i))/m*dt
        NEXT i
        IF jt=nf+1 THEN
          plt=0: kk=0
          FOR i=1 TO n/2-1: e2=e2+v(i)*v(i): NEXT i
          GCOL 0: MOVE 20, 370
          PRINT "Reflects "; INT(10000*e2/e1)/100; " % of incident energy"
          * REFRESH ON
        ENDIF
      ENDWHILE
      ENDPROC