title: Solving coupled Differential Equation by Matlab or by calculations
body: <p>Solving coupled non linear differential equation by  Mat-lab or  by calculations </p>
  
  <pre><code>equation 1:   x'(t) = -a* x(t) /(x(t) + y(t))
  equation 2:   y'(t) = -b* y(t) /(x(t) + y(t))
  </code></pre>
  
  <p>I tried in <a href="http://www.wolframalpha.com/input/?i=DSolve%5B%7Bx%27%5Bt%5D%20==%20-a%2ax%5Bt%5D%20/%28x%5Bt%5D%2by%5Bt%5D%29,%20y%27%5Bt%5D%20==%20-b%2ay%5Bt%5D%20/%28x%5Bt%5D%2by%5Bt%5D%29%7D,%20%7Bx,%20y%7D,%20t%5D" rel="nofollow">mathematica</a> but got a very comlicated solution.</p>
  
  <pre><code>Solve[{x'[t] == -a* x[t] /(x[t] + y[t]), y'[t] == -b* y[t] /(x[t] + y[t])}, {x, y}, t]
  </code></pre>
  
  <p>How can I plot it?</p>
  
  <p>My initial conditions are</p>
  
  <pre><code> x(0) = xo
   y(0) = yo
  </code></pre>
  
  <p>Also, a and b are constants.</p>
  
  <p>I have to plot x and y wrt t after inserting values of  a and b . ( a= 2 , b =5 say )</p>