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Hi,<div><br></div><div>I've got a problem to solve a non linear differential equation, which is :</div><div><br></div><div>y1'=A*(1-sin(y2))/(pi/2-y2)-B*y1^2</div><div>y2'=y1</div><div><br></div><div><br></div><div>I'm using ode : </div><div><br></div><div><pre style="font-family:Monospaced;font-style:normal;font-size:14.0;"><span style="color:rgb(176,24,19);">function</span> <span style="color:rgb(74,85,219);">[</span><span style="color:rgb(131,67,16);font-weight:bold;">Xprime</span><span style="color:rgb(74,85,219);">]</span><span style="color:rgb(92,92,92);">=</span><span style="color:rgb(0,0,0);text-decoration:underline;">VanDerPol</span><span style="color:rgb(74,85,219);">(</span><span style="color:rgb(131,67,16);font-weight:bold;">t</span><span style="color:rgb(0,0,0);">, </span><span style="color:rgb(131,67,16);font-weight:bold;">X</span><span style="color:rgb(74,85,219);">)</span>
<span style="color:rgb(131,67,16);font-weight:bold;">Xprime</span><span style="color:rgb(74,85,219);">(</span><span style="color:rgb(188,143,143);">1</span><span style="color:rgb(74,85,219);">)</span> <span style="color:rgb(92,92,92);">=</span> <span style="color:rgb(131,67,16);font-weight:bold;">X</span><span style="color:rgb(74,85,219);">(</span><span style="color:rgb(188,143,143);">2</span><span style="color:rgb(74,85,219);">)</span>
<span style="color:rgb(131,67,16);font-weight:bold;">Xprime</span><span style="color:rgb(74,85,219);">(</span><span style="color:rgb(188,143,143);">2</span><span style="color:rgb(74,85,219);">)</span> <span style="color:rgb(92,92,92);">=</span> <span style="color:rgb(0,0,0);">g</span><span style="color:rgb(92,92,92);">/</span><span style="color:rgb(0,0,0);">R</span><span style="color:rgb(92,92,92);">*</span><span style="color:rgb(74,85,219);">(</span><span style="color:rgb(188,143,143);">1</span><span style="color:rgb(92,92,92);">-</span><span style="color:rgb(50,185,185);">sin</span><span style="color:rgb(74,85,219);">(</span><span style="color:rgb(131,67,16);font-weight:bold;">X</span><span style="color:rgb(74,85,219);">(</span><span style="color:rgb(188,143,143);">1</span><span style="color:rgb(74,85,219);">)</span><span style="color:rgb(74,85,219);">)</span><span style="color:rgb(74,85,219);">)</span><span style="color:rgb(92,92,92);">/</span><span style="color:rgb(74,85,219);">(</span><span style="color:rgb(218,112,214);">%pi</span><span style="color:rgb(92,92,92);">/</span><span style="color:rgb(188,143,143);">2</span><span style="color:rgb(92,92,92);">-</span><span style="color:rgb(131,67,16);font-weight:bold;">X</span><span style="color:rgb(74,85,219);">(</span><span style="color:rgb(188,143,143);">1</span><span style="color:rgb(74,85,219);">)</span><span style="color:rgb(74,85,219);">)</span><span style="color:rgb(92,92,92);">-</span><span style="color:rgb(0,0,0);">deltaP</span><span style="color:rgb(92,92,92);">/</span><span style="color:rgb(74,85,219);">(</span><span style="color:rgb(0,0,0);">B</span><span style="color:rgb(92,92,92);">*</span><span style="color:rgb(74,85,219);">(</span><span style="color:rgb(218,112,214);">%pi</span><span style="color:rgb(92,92,92);">/</span><span style="color:rgb(188,143,143);">2</span><span style="color:rgb(92,92,92);">-</span><span style="color:rgb(131,67,16);font-weight:bold;">X</span><span style="color:rgb(74,85,219);">(</span><span style="color:rgb(188,143,143);">1</span><span style="color:rgb(74,85,219);">)</span><span style="color:rgb(74,85,219);">)</span><span style="color:rgb(74,85,219);">)</span>
<span style="color:rgb(176,24,19);">endfunction</span>
<span style="color:rgb(0,0,0);">t</span><span style="color:rgb(92,92,92);">=</span><span style="color:rgb(174,92,176);text-decoration:underline;">linspace</span><span style="color:rgb(74,85,219);">(</span><span style="color:rgb(188,143,143);">0</span><span style="color:rgb(0,0,0);">,</span><span style="color:rgb(188,143,143);">4</span><span style="color:rgb(0,0,0);">,</span><span style="color:rgb(188,143,143);">3000</span><span style="color:rgb(74,85,219);">)</span><span style="color:rgb(0,0,0);">;</span> <span style="color:rgb(0,0,0);">X0</span><span style="color:rgb(92,92,92);">=</span><span style="color:rgb(74,85,219);">[</span><span style="color:rgb(188,143,143);">85</span><span style="color:rgb(92,92,92);">*</span><span style="color:rgb(218,112,214);">%pi</span><span style="color:rgb(92,92,92);">/</span><span style="color:rgb(188,143,143);">180</span><span style="color:rgb(0,0,0);">;</span><span style="color:rgb(188,143,143);">0</span><span style="color:rgb(74,85,219);">]</span><span style="color:rgb(0,0,0);">;</span>
<span style="color:rgb(74,85,219);">[</span><span style="color:rgb(0,0,0);">u</span><span style="color:rgb(74,85,219);">]</span><span style="color:rgb(92,92,92);">=</span><span style="color:rgb(50,185,185);">ode</span><span style="color:rgb(74,85,219);">(</span><span style="color:rgb(0,0,0);">X0</span><span style="color:rgb(0,0,0);">,</span><span style="color:rgb(188,143,143);">0</span><span style="color:rgb(0,0,0);">,</span><span style="color:rgb(0,0,0);">t</span><span style="color:rgb(0,0,0);">,</span><span style="color:rgb(0,0,0);text-decoration:underline;">VanDerPol</span><span style="color:rgb(74,85,219);">)</span><span style="color:rgb(0,0,0);">;</span>
<span style="color:rgb(174,92,176);text-decoration:underline;">plot</span><span style="color:rgb(74,85,219);">(</span><span style="color:rgb(0,0,0);">t</span><span style="color:rgb(0,0,0);">,</span><span style="color:rgb(0,0,0);">u</span><span style="color:rgb(74,85,219);">(</span><span style="color:rgb(188,143,143);">1</span><span style="color:rgb(0,0,0);">,</span><span style="color:rgb(255,170,0);">:</span><span style="color:rgb(74,85,219);">)</span><span style="color:rgb(92,92,92);">*</span><span style="color:rgb(188,143,143);">180</span><span style="color:rgb(92,92,92);">/</span><span style="color:rgb(218,112,214);">%pi</span><span style="color:rgb(0,0,0);">,</span><span style="color:rgb(188,143,143);">'</span><span style="color:rgb(188,143,143);">r</span><span style="color:rgb(188,143,143);">'</span><span style="color:rgb(74,85,219);">)</span>
<span style="color:rgb(174,92,176);text-decoration:underline;">plot</span><span style="color:rgb(74,85,219);">(</span><span style="color:rgb(0,0,0);">t</span><span style="color:rgb(0,0,0);">,</span><span style="color:rgb(0,0,0);">R</span><span style="color:rgb(92,92,92);">*</span><span style="color:rgb(0,0,0);">u</span><span style="color:rgb(74,85,219);">(</span><span style="color:rgb(188,143,143);">2</span><span style="color:rgb(0,0,0);">,</span><span style="color:rgb(255,170,0);">:</span><span style="color:rgb(74,85,219);">)</span><span style="color:rgb(74,85,219);">)</span></pre><pre style="font-family:Monospaced;font-style:normal;font-size:14.0;"><span style="color:rgb(74,85,219);"><br></span></pre><pre style="font-family:Monospaced;font-style:normal;font-size:14.0;"><span style="color:rgb(74,85,219);"><br></span></pre><pre style="font-family:Monospaced;font-style:normal;font-size:14.0;"><span style="color:rgb(74,85,219);">but it doesn't work.</span></pre><pre style="font-family:Monospaced;font-style:normal;font-size:14.0;"><font class="Apple-style-span" color="#4a55db"><br></font></pre><pre style="font-family:Monospaced;font-style:normal;font-size:14.0;"><font class="Apple-style-span" color="#4a55db">Do you know why?</font></pre><pre style="font-family:Monospaced;font-style:normal;font-size:14.0;"><font class="Apple-style-span" color="#4a55db"><br></font></pre><pre style="font-family:Monospaced;font-style:normal;font-size:14.0;"><font class="Apple-style-span" color="#4a55db">Best regards.</font></pre></div> </div></body>
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