hi i was doing my assignment but i cant get the variable vn to save in a vector so i can plot it at the end just wondering how i can do that. everything else works fine and when i try to put Vn (k) does not work? please help

%%Matlab Assignment 1
%%Problem 4
clc;
clear;
close all;

% Volume of the dam
%vd=SA*d
vd=242760*20*10^-3

%Water Out of lake every day
wold=5.26*60*60*24*10^-3

%Volume of Lake at start of november
Nv=242760*12*10^-3

%Volume of lake at %
p100=4855200*10^-3
p90=4855200*0.9*10^-3
p70=4855200*0.7*10^-3
p50=4855200*0.5*10^-3
p30=4855200*0.3*10^-3

a=0
b=0

%flow rates for rivers
fr=xlsread('data_Problem4_RiverDischarge.xls');

for k=1:length(fr) %index for vector of fr
    Nv=Nv+(fr(k)-wold)
        if Nv>=p100
        wold=3*(5.26*60*60*24*10^-3)
        display ('Alert Dam is at 100 Percent Capacity')
        a=a+1
        elseif Nv>=p90 & Nv<p100
        wold=3*(5.26*60*60*24*10^-3)
        elseif Nv<p90 & Nv>p70
        wold=wold            
        elseif Nv<=p70 & Nv>=p50
        wold=5.26*60*60*24*10^-3
        elseif Nv<p50 & Nv>p30
        wold=wold
        else Nv<=p30
        display ('The dam is to low close the outflow')
        wold=0
        b=b+1
        end
end

fprintf ('The number of times the dam was over capacity is %5.0f \n', a)
fprintf ('The number of times the dam was under 30 percent capacity is %5.0f \n', b)

[Walter Roberson]

else Nv<=p30

means to evaluate the logical expression

Nv<=p30

and display the result in the command window.

If you are sure the condition holds at that point then make it a comment; if the condition might not hold then make it an "elseif" (and worry about if none of the conditions hold)

Question: why are you not initializing Nv ?

[ben]

hey sorry just posted the full code, it works totally in the command window however i cant get the variables for Nv to save in a matrics or vector so i can plot the results.

Answer 1

[Walter Roberson]

You do not create a variable named Vn, so you cannot save it.

[Walter Roberson]

Change

Nv=242760*12*10^-3

to

Nv(1) = 242760*12*10^-3

And change

Nv=Nv+(fr(k)-wold)

to

Nv(k+1) = Nv(k) + (fr(k)-wold)

Then in the rest of the loop where you refer to Nv, instead refer to Nv(k+1)

Answer 2

[ben]

thanks very much.