How to write the equivalent of an 'until loop' in matlab?

if T>=673
  U=(4*11.3)/(5000*0.0762);
"until T=593"
else U=1/(298-T);
end;

Basically I want to be able to say until T = 593 but in a way understood by Matlab.

The whole code is such:

function f = dndw(w,n)

b=n(1);
o=n(2);
bd=n(3);
h=n(4);
co=n(5);
T=n(6);

k1=(85)*exp(-53100/(8.314*T));
k2=(9944444.444)*exp(-128300/(8.314*T));
k3=(8722222.222)*exp(-154700/(8.314*T));
k4=(95000000)*exp(-156000/(8.314*T));

np=4.317;
nn=639.2;
nt=b+o+bd+h+np+co+nn;
P=202.650;

pb=(b/nt)*P;
po=(o/nt)*P;
pbd=(b/nt)*P;

r1=(k1*k2*(po^0.5)*pb)/(0.5*k1*pb+k2*(po^0.5));
r2=k3*(po^0.7)*(pb^0.25)*(pbd^-0.86);
r3=k4*(po^0.25)*(pbd^0.85);

dbdw=-r1-r2;
dodw=-0.5*r1-6*r2-5.5*r3;
dbddw=r1-r3;
dhdw=r1+4*r2+3*r3;
dcodw=4*r2+4*r3;
***dTdw=(U*(493-T)*((165170.736*r1)+(2711247*r2)+(2431510*r3)))/(40*nt)***;

f=[dbdw;dodw;dbddw;dhdw;dcodw;dTdw];
end

Thanks!

Answer 1

[Roger Stafford]

To reproduce the equivalent of repeat --- until in C, do this:

   b = true;
   while b
     do the loop computations
     b = ~until % <-- Form the logical "NOT" of the desired "until" condition
   end

[Walter Roberson]

Alternately but equivalently:

while true
  do the loop computations
  if TheCondition
    break;
  end
end

[Kavya]

but @Walter Roberson, MATLAB says we can't use "break" statement in the if block?

it shows error. can you suggest other way we could represent repeat-until loop?

the loop limit is not known but it must terminate when a particular condition is reached.

[Image Analyst]

You certainly CAN use break in an if block as long as the if block is inside a while or for block. You should also use a failsafe to prevent an infinite loop. Here is an example:

% Demonstration of how to avoid an infinite loop by setting up a failsafe.
% Set up a failsafe
maxIterations = 100; % Way more than you think it would ever need.
loopCounter = 0;
% Now loop until we obtain the required condition: a random number equals exactly 0.5.
% If that never happens, the failsafe will kick us out of the loop so we do not get an infinite loop.
r = nan; % Initialize so we can enter the loop the first time.
while (r ~= 0.5) && loopCounter < maxIterations
    loopCounter = loopCounter + 1;
    fprintf('Iteration #%d.\n', loopCounter)
    % Now break if some other condition becomes true somehow.
    someOtherCondition = whatever;
    if someOtherCondition
        break;
    end
    % Get another, new random value.
    r = rand;
end
% Alert user if we exited normally, or if the failsafe kicked us out to avoid an infinite loop.
if loopCounter < maxIterations
    % Then the loop found the condition and exited early, which means normally.
    fprintf('Loop exited normally after %d iterations.\n', loopCounter);
else
    % Then the loop never found the condition and exited when the number of iterations
    % hit the maximum number of iterations allowed, which means abnormally.
    fprintf('Loop exited abnormally after iterating the maximimum number of iterations (%d) without obtaining the exit criteria.\n', maxIterations);
end
fprintf('All done after %d iterations.\n', loopCounter)

Answer 2

[Azzi Abdelmalek]

while loop

[McNugget]

I've tried but perhaps I'm not understanding. Could you perhaps show me how?

Thanks!

[Azzi Abdelmalek]

%Example: calcul the sum s= 1+2+3+...+n  with s<=1000
s=0;
k=1;
while k<1000
    k=2*k
    s=s+k
end