Index exceeds matrix dimensions

Question

hasan damaj 2019-9-29

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https://ww2.mathworks.cn/matlabcentral/answers/482709-index-exceeds-matrix-dimensions

评论： hasan damaj 2019-11-29

% flow m3/s
Q = 20;
% slope  m/m
So = 0.0001;
% side slope m/m 
z = 2;
% manning number 
n = 0.015;
b = 10; % width of channel m
g = 9.81; % gravity force m/s2
N = 4;
ys = 1;
yend = 2;
dy = abs((ys-yend)/N);
y(1) = ys;
% A(1) = ;x
for i = 1:N+1
    if i == 1
      y(i) = ys;
    else 
    y(i)= y(i-1) + dy;
    end
    A(i) = (b + y(i)*z)*(y(i));
    P(i) = b + 2*y(i)*sqrt(1+z^2);
    R(i) = A(i) / P(i);
    V(i) = Q / A(i);
    E(i) = y(i) +  V(i)^2 / (2*g);
    if i == 1;
      dE(i) = 0;
    else
        dE(i) = E(i)-E(i-1);  
    end
    dE
    Se(i) = (V(i)^2)* (n^2)/(R(i)^(4/3))
    if i > 1
        Sav(i) = (Se(i) + Se(i+1))/2
    else 
        Sav(i) = 0
    end
    if i > 1
        dx = dE(i)/(So - Sav(i))
    else 
        dx = 0
    end
    if i > 1
        x (i) = dx(i) + dx(i-1);
    else 
        x(i)= 0
    end
end

its giving me on line where dE(i) =E(i) -E(i+1)

Sav(i) =(Se(i) + Se(i+1))/2

index exceed matrix dimension

How do i solve the issue???

thank you

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hasan damaj 2019-9-30

Mr. Adam,

i already correct the continued and finished it.

if i want to put the variable of

y A P R V E dE Se Sav dx x

in a matrix in for of a table .. what is the required code.??

this process is called water surface profile using direct step method.(Civil Engineering).

also i need to plot the vales of x with respect to y.???

if you just help me i will be gratefull.

Adam Danz 2019-9-30

See answer.

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Answer 1

Csaba 2019-9-29

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/482709-index-exceeds-matrix-dimensions#answer_394006

在 MATLAB Online 中打开

    E(i) = y(i) +  V(i)^2 / (2*g);
    if i == 1;
      dE(i) = 0;
    else
        ,dE(i) = E(i)-E(i+1);  ,
    end

You are defining E(i) in the for loop, and later in the same for loop you are referencing to E(i+1) (before it was definied). Where the hell prograsm should know what E(i+1) would be in the next circle when you will define it?

This code is incorrect.

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Csaba 2019-9-30

编辑：Csaba 2019-9-30

在 MATLAB Online 中打开

I guess you want something like this!

% flow m3/s
Q = 20;
% slope  m/m
So = 0.0001;
% side slope m/m 
z = 2;
% manning number 
n = 0.015;
b = 10; % width of channel m
g = 9.81; % gravity force m/s2
N = 4;
ys = 1;
yend = 2;
dy = abs((ys-yend)/N);
y(1) = ys;
dE(1) = 0;  
Sav(1) = 0;
% A(1) = ;x
% for i = 1:N+1
%     if i == 1
%     y(i) = ys;
%     else 
%     y(i)= y(i-1) + dy;
%     end
for i=2:N+1
    y(i)= y(i-1) + dy;
    A(i) = (b + y(i)*z)*(y(i));
    P(i) = b + 2*y(i)*sqrt(1+z^2);
    R(i) = A(i) / P(i);
    V(i) = Q / A(i);
    E(i) = y(i) +  V(i)^2 / (2*g);
    dE(i) = E(i)-E(i-1);
    Se(i) = (V(i)^2)* (n^2)/(R(i)^(4/3))
    Sav(i) = (Se(i) + Se(i-1))/2;
    dx(i) = dE(i)/(So - Sav(i));     % I guess you want dx(i) intead of just dx
    x (i) = dx(i) + dx(i-1);
    
    
    
    
    % You do not need all of this below because now (after my corrections)
    % i runs from 2 and all i=1 values are assigned before the for cycle!
    % all others are now listed above!
%     if i == 1;
%       dE(i) = 0;
%     else
%         dE(i) = E(i)-E(i-1);  
%     end
%     dE
%     Se(i) = (V(i)^2)* (n^2)/(R(i)^(4/3))
%     if i > 1
%         Sav(i) = (Se(i) + Se(i+1))/2
%     else 
%         Sav(i) = 0
%     end
%     if i > 1
%         dx = dE(i)/(So - Sav(i))
%     else 
%         dx = 0
%     end
%     if i > 1
%         x (i) = dx(i) + dx(i-1);
%     else 
%         x(i)= 0
%     end
end
plot(x,y);

hasan damaj 2019-11-29

above a fortran code

how to transfer to matlab code?

thank you

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Answer 2

Adam Danz 2019-9-30

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链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/482709-index-exceeds-matrix-dimensions#answer_394150

在 MATLAB Online 中打开

"if i want to put the variable of

y A P R V E dE Se Sav dx x

in a matrix in for of a table .. what is the required code.??"

Those variables are row vectors of equal length and can be concatenated vertically into a matrix like this:

out = [y;A;P;R;V;E;dE;Se;Sav;dx;x];

But to follow the principles of Tidy Data, each column of a matrix should be a variable and each row an observation. The matrix would be transposed.

out = [y;A;P;R;V;E;dE;Se;Sav;dx;x].'; 
%                                 ^^

Better yet, I recommend using a table

T = array2table([y;A;P;R;V;E;dE;Se;Sav;dx;x].',...
    'VariableNames',{'y','A','P','R','V','E','dE','Se','Sav','dx','x'})

"also i need to plot the vales of x with respect to y."

Assuming you've created the table above,

plot(T.x,T.y,'o-')

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hasan damaj 2019-9-30

Thank you mr Adam for the help.

but regarding the last code which is plot,

what is o-???

Adam Danz 2019-9-30

It's the linespec of the plot

https://www.mathworks.com/help/matlab/ref/plot.html#d117e1049403

It plots with lines (-) and circle markers (o).

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