Why don't graphics appear for this code?

Why don't graphics appear for this code?

% Variáveis
m = 112.34;
temp = 25;
ISC = 7.8;
VTR = 0.0257;
VT = 0.0257;
VCA = 32.7;
GR = 1000;
G = 700;

% Cálculo do IR

IR = 1000 * (ISC / (2.718*exp(VCA/(m*VTR))-1))

for V = 0:1:VCA

V1 = V*2

%Carcular a potencia máxima para G=1000
P = V1*IR*35
end

figure(1)
h=plot(V1,P);
set(h,'color',rand(1,3),'linewidth',2);
hold on
axis([0 200 0 40])
xlabel('Tensão')
ylabel('Potência')
title('Curva P-V')

Answer 1

[Walter Roberson]

Each time through the loop you replace V1 and P, so at the end of the loop you only have a single point to plot.

Try

V1 = (0:1:VCA).*2; P = V1.*IR.*35;

with no loop.

Answer 2

[Nuno]

Why i can´t make loop?

[Walter Roberson]

You _can_ do it with a loop, provided that you store the V1 and P value that results from each loop. You aren't doing that now: each time through the loop, you are overwriting the previously calculated value.

[Matt Tearle]

What Walter was saying above is that you don't *need* to have a loop -- his solution does the same thing, cleaner and simpler.

As an aside, note that 0:1:VCA will give you whole numbers from 0 up to 32, because VCA is 32.7. That is, the range operator in MATLAB is essentially "<=". Obviously I don't know your intention -- just wanted to make sure you're aware of that.

Answer 3

[Nuno]

But if i change to V1= 0:0.1:VCA appear error in P=V1.*IR.*35...

[Walter Roberson]

Notice I used

V1 = (0:1:VCA).*2

But even without the multiplication by 2, I do not find any obvious error in P=V1.*IR.*35 . What error do you observe?

[Matt Tearle]

Works fine for me:

m = 112.34;

temp = 25;

ISC = 7.8;

VTR = 0.0257;

VT = 0.0257;

VCA = 32.7;

GR = 1000;

G = 700;

% Cálculo do IR

IR = 1000 * (ISC / (2.718*exp(VCA/(m*VTR))-1));

V = 0:1:VCA;

V1 = V*2;

%Carcular a potencia máxima para G=1000

P = V1*IR*35;

figure(1)

h=plot(V1,P);

set(h,'color',rand(1,3),'linewidth',2);

hold on

axis([0 200 0 40])

xlabel('Tensão')

ylabel('Potência')

title('Curva P-V')

Answer 4

[Nuno]

Yes, the code works... Thanks! But now i have a new problem...

When i complile de program, the graphs should give a value of voltage (V) up to 32,7 but the value is ~12,5. Why?

Code:

% Variáveis
m = 112.34;
temp = 25;
ISC = 7.8;
VTR = 0.0257;
VT = 0.0257;
VCA = 32.7;
GR = 1000;
G = 700;

% Cálculo do IR
IR = 1000 * (ISC / (2.718*exp(VCA/(m*VTR))-1));

V1 = (0:0.1:VCA);

ICC = ISC * (G/GR);
I = ICC - IR.*(2.718.*exp(V1./(m.*VT))-1);

ICC1 = ISC * ((G+100)/GR);
I1 = ICC1 - IR.*(2.718.*exp(V1./(m.*VT))-1);

ICC2 = ISC * ((G+200)/GR);
I2 = ICC2 - IR.*(2.718.*exp(V1./(m.*VT))-1);

ICC3 = ISC * ((G+300)/GR);
I3 = ICC3 - IR.*(2.718.*exp(V1./(m*VT))-1);

ICC4 = ISC * ((G+400)/GR);
I4 = ICC4 - IR.*(2.718.*exp(V1./(m*VT))-1);

%Carcular a potencia máxima para G=1000
P = V1.*I3;

figure(1)
j=plot(V1,P);
set(j,'color',rand(1,3),'linewidth',2);
hold on
axis([0 40 0 100])
xlabel('Tensão(V)')
ylabel('Potência')
title('Curva P-V')

figure(2)
h=plot(V1,I,V1,I1,V1,I2,V1,I3,V1,I4);
set(h,'color',rand(1,3),'linewidth',2);
hold on
axis([0 40 0 40])
xlabel('Tensão(V)')
ylabel('Corrente')
title('Curva I-V')

[Walter Roberson]

The voltage does go up to there, but the axis() call forces all output values below 0 to be discarded.

I do not know what is being calculated (and would not necessarily understand it if you explained).

Question: why are you multiplying those values by 2.718 ? Isn't that just exp(1) ? So why not just add 1 to the value inside the exp() and not do the multiplication?

[Nuno]

I calculate the diode current in a photovoltaic circuit.

2.718 is a nepper number and exp() is exponensial...

I can review the calculations...

[Walter Roberson]

The nepper number that is approximately 2.718 *is* exactly exp(1) .

[Nuno]

Ok... Stupid error :(

But gives error if i change to: I = ICC - IR.*(2.718^(V1./(m.*VT))-1);

[Walter Roberson]

Use .^ instead of ^

Also, exp(expression) would be clearer than 2.718.^(expression)

[Matt Tearle]

And, more importantly, correct. 2.718^x is an inaccurate version of exp(x).

[Nuno]

The error is in another count... Thanks for the help...