I am not able to debug my script as follows

%%Prefault System;
Pb=25e3;
%Transfer Reactance
X=1i*0.3+(1i*0.2/2);
%Defining Values;
E=1.03;
V=1.0;
%Max Power
Pmax=(abs(E)*abs(V))/abs(X);
%Electrical Power;
deliveredP=20e3;
Pele = deliveredP/Pb;
%Initial Load Angle;
Delta0=asin(Pele/Pmax);
Delta0deg=rad2deg(Delta0);

%%System under fault
%Finding delta of fault.
X2=1i*0.3+1i*0.2+((1i*0.4*1i*0.2)/1i*0.1);
DelFault=asin(Pele*X2/E*V);

%%Post Fault System
%Finding transfer reactance
XT=1i*0.3+1i*0.2;
%Finding the delta post fault.
DelPFault=asin(Pele*XT/E*V);
%Calculation of the swing curve
%Kineitic Energy
H=2.56;
freq=60;
M=H/(150*freq);
%Interval time
IT=0.1;
%defining the constant
C=(IT^2)/M;
%Delta of the swing bus
DeltaSW=0;
radDeltaSW=deg2rad(DeltaSW);

%%Calculating the swing curve
%Accelerating power at the beginning of the time interval
Pa1=0;
Pa2=Pmax-0.935*sin(DelFault);
%Aver accelerating power
PaAVE1=(Pa1+Pa2)/2;
%calculating change in the load angle in the time interval;
cPaAVE1=C*PaAVE;

Unrecognized function or variable 'PaAVE'.

changeDel1=radDeltaSW+cPaAVE;
%Delta and acc power at the beginning(0.1)
Delta1=Delta0+changeDel1;
Pa3=Pmax-0.935*sin(Delta1);
PaAVE2=(Pa2+Pa3)/2;
cPaAVE1=C*cPaAVE;
changeDel2=changeDel1+cPaAVE1;
%0.2sec
Delta2=Delta0+changeDel2;
Pa4=Pmax-0.935*sin(Delta2);
PaAVE3=(Pa3+Pa4)/2;
cPaAVE2=C*cPaAVE1;
changeDel3=changeDel2+cPaAVE2;
%0.3sec
Delta3=Delta1+changeDel3;
Pa5=Pmax-0.935*sin(Delta3);
PaAVE4=(Pa3+Pa4)/2;
cPaAVE4=C*cPaAVE2;
changeDel4=changeDel3+cPaAVE3;
%0.4sec
Delta4=Delta3+changeDel4;
Pa1=Pmax-0.935*sin(Delta4);
Pa2=Pmax-2.06*sin(Delta4);
PaAVE5=(Pa1+Pa2)/2;
cPaAVE5=C*PaAVE5;
changeDel5=changeDel4+cPaAVE4;
%0.5sec
Delta5=Delta4+changeDel5;
Pa5=Pmax-2.06*sin(Delta5);
PaAVE6=(Pa4+Pa5)/2;
cPaAVE5=C*PaAVE5;
changeDel6=changeDel5+cPaAVE5;
%0.6sec
Delta6=Delta4+changeDel5;
Pa6=Pmax-2.06*sin(Delta4);
PaAVE6=(Pa5+Pa6)/2;
cPaAVE6=C*PaAVE6;
changeDel6=changeDel5+cPaAVE5;
%0.7sec
Delta7=Delta5+changeDel6;
Pa7=Pmax-2.06*sin(Delta7);
PaAVE7=(Pa6+Pa7)/2;
cPaAVE7=C*PaAVE6;
changeDel7=changeDel6+cPaAVE7;
%0.8sec
Delta8=Delta5+changeDel6;
Pa8=Pmax-2.06*sin(Delta8);
PaAVE8=(Pa7+Pa8)/2;
cPaAVE8=C*PaAVE8;
changeDel8=changeDel7+cPaAVE7;
%0.9sec
Delta9=Delta6+changeDel7;
Pa9=Pmax-2.06*sin(Delta9);
PaAVE9=(Pa8+Pa9)/2;
cPaAVE9=C*PaAVE9;
changeDel9=changeDel8+cPaAVE8;
%1.0sec
Delta10=Delta7+changeDel8;

Answer 1

[Walter Roberson]

PaAVE1=(Pa1+Pa2)/2;

You assign to PaAVE1 but you do not use PaAVE1 afterwards

cPaAVE1=C*PaAVE;

No variable PaAVE is defined.

You do not use cPaAVE1 before it is overwritten.

changeDel1=radDeltaSW+cPaAVE;

No variable cPaAVE is defined.

PaAVE2=(Pa2+Pa3)/2;
cPaAVE1=C*cPaAVE;

You overwrite cPaAVE1. My guess is that you want to write to cPaAVE2 and use that variable in the following code.