Why is this error popping up for this script?

P1 = 101 %pressure in kpa

P1 = 101

T1 = 298%temperature in kelvin

T1 = 298

n = 1.4

n = 1.4000

Cp = 1.004

Cp = 1.0040

Cv = 0.717

Cv = 0.7170

R = 0.287 %gas constant in kJ/kg*k

R = 0.2870

v1 = R * T1/P1 %specific volume in m^3/kg

v1 = 0.8468

IsentConst1 = P1 * v1^n

IsentConst1 = 80.0219

P2 = 28 * 101 %outlet compressor/inlet combuster pressure

P2 = 2828

v2 = (P1 *v1^n / 2)^(1-n)

v2 = 0.2286

T2 = P2 * v2 / R

T2 = 2.2528e+03

Wc = Cp * (T2 - T1)

Wc = 1.9626e+03

P3 = P2

P3 = 2828

T3 = 2260 

T3 = 2260

v3 = R * T3 / P3

v3 = 0.2294

IsentConst2 = P3 * v3^n

IsentConst2 = 359.9107

T4 = (Wc / Cp) + T3

T4 = 4.2148e+03

v4 = ((P3 * v3^n)/(R * T4)^(1/n-1))

v4 = 2.7350e+03

P4 = R * T4 /v4

P4 = 0.4423

IsentConst3 =  P4 * v4^n

IsentConst3 = 2.8671e+04

u4 = Cv * T4

u4 = 3.0220e+03

h4 = u4 + P4 * v4

h4 = 4.2317e+03

P5 = P1

P5 = 101

v5 = (P4 *v4^n / P5)^(1/n)

v5 = 56.5236

T5 = P5 *v5 / R

T5 = 1.9892e+04

u5 = Cv * T5

u5 = 1.4262e+04

h5 = u5 + P5 * v5

h5 = 1.9971e+04

dh = (h4 - h5)*1000 %performance parameter

dh = -1.5739e+07

i = 0;
for v = v1:-0.001:v2
    i = i + 1;
v = v1:0.001:v2
P(i) = IsentConst1 \ v.^n;
end

v =

  1×0 empty double row vector

Unable to perform assignment because the indices on the left side are not compatible with the size of the right side.

v = v1:-0.001:v2;
plot(v,P,'r','lineWidth',1.5)

Answer 1

[KSSV]

In the loop:

i = 0;
for v = v1:-0.001:v2
    i = i + 1;
    v = v1:0.001:v2   %<---- this is empty matrix. 
P(i) = IsentConst1 \ v.^n;  %<---- as v is empty, result is empty matrix and you cannot save 
end

Work around:

 v = v1:-0.001:v2 ;

Then this line:

 IsentConst1 \ v.^n

will be an array and you cannot save it into a single element.

You have to use:

P{i} = IsentConst1 \ v.^n;

Prior to this:

1. Think is your code correct. I don't think so. Use logic.
2. DEbug the code.
3. Read about the problem.
4. Take basic course in MATLAB.

[Nick Olibrice]

how could i plot P-v diagram, error says there is no function of P

[KSSV]

clc; clear all ;
P1 = 101 %pressure in kpa

P1 = 101

T1 = 298%temperature in kelvin

T1 = 298

n = 1.4

n = 1.4000

Cp = 1.004

Cp = 1.0040

Cv = 0.717

Cv = 0.7170

R = 0.287 %gas constant in kJ/kg*k

R = 0.2870

v1 = R * T1/P1 %specific volume in m^3/kg

v1 = 0.8468

IsentConst1 = P1 * v1^n

IsentConst1 = 80.0219

P2 = 28 * 101 %outlet compressor/inlet combuster pressure

P2 = 2828

v2 = (P1 *v1^n / 2)^(1-n)

v2 = 0.2286

T2 = P2 * v2 / R

T2 = 2.2528e+03

Wc = Cp * (T2 - T1)

Wc = 1.9626e+03

P3 = P2

P3 = 2828

T3 = 2260 

T3 = 2260

v3 = R * T3 / P3

v3 = 0.2294

IsentConst2 = P3 * v3^n

IsentConst2 = 359.9107

T4 = (Wc / Cp) + T3

T4 = 4.2148e+03

v4 = ((P3 * v3^n)/(R * T4)^(1/n-1))

v4 = 2.7350e+03

P4 = R * T4 /v4

P4 = 0.4423

IsentConst3 =  P4 * v4^n

IsentConst3 = 2.8671e+04

u4 = Cv * T4

u4 = 3.0220e+03

h4 = u4 + P4 * v4

h4 = 4.2317e+03

P5 = P1

P5 = 101

v5 = (P4 *v4^n / P5)^(1/n)

v5 = 56.5236

T5 = P5 *v5 / R

T5 = 1.9892e+04

u5 = Cv * T5

u5 = 1.4262e+04

h5 = u5 + P5 * v5

h5 = 1.9971e+04

dh = (h5 - h4)*1000 %performance parameter

dh = 1.5739e+07

i = 0;

for v = v1:-0.001:v2
    i = i + 1;
    P(i) = IsentConst1 \ v.^n;  %<---- as v is empty, result is empty matrix and you cannot save 
end
v = v1:-0.001:v2;
plot(v,P,'r','lineWidth',1.5)