title: Expected ‘double *’ but argument is of type ‘double **’
body: <p>Hello everyone and thanks in advance.
  Im trying to write a function in C for Gauss-Legendre quadrature - numerical method for integrating - and I have to apply it for 2 cases, one whose interval is converted to [-1,1] and another case whose interval is yet divided again in four parts.
  As both uses the same tabled numbers for the weights and abscissas, I have made arrays for both, and the only difference between them would be the function for dividing(or redividing) the interval.
  The thing is that, as for each I will have different applications on the function I want to integrate (which is in case erf) and different multipliers
  (I won t go in detail, it is intrinsic mathematical part of the method) I`ve a function:</p>
  
  <pre><code>void adapt(double a, double b, double *ptrt, double *ptrm, double x)
  {
     *ptrt=1/2*(x*(b-a)+a+b);
     *ptrm=(b-a)/2;
  }
  </code></pre>
  
  <p>Where a and b stands for the beggingin and the ending of the original interval, x for the the tabled gauss-legendre value of x and the the pointers would return numbers I need to use in the formulae at the quadrature function:</p>
  
  <pre><code>double gauss(double a, double b)
  {
  int i;
  double I, t, m,  p[16],  x[16];
  double *ptrt, *ptrm;
  ptrt=&amp;t;
  ptrm=&amp;m;
  I=t=m=0.0;
  x[1]=0.0000000000000000; x[2]=-0.2011940939974345; x[3]=0.2011940939974345;
  x[4]=-0.3941513470775634; x[5]=0.3941513470775634; x[6]=-0.5709721726085388;
  x[7]=0.5709721726085388; x[8]=-0.7244177313601701; x[9]=0.7244177313601701;
  x[10]=-0.8482065834104272; x[11]=0.8482065834104272; x[12]=-0.9372733924007060 ;
  x[13]=0.9372733924007060; x[14]=-0.9879925180204854; x[15]=0.9879925180204854 ;
  
  p[1]=0.2025782419255613; p[2]=0.1984314853271116; p[3]=0.1984314853271116;
  p[4]=0.1861610000155622; p[5]=0.1861610000155622; p[6]=0.1662692058169939;
  p[7]=0.1662692058169939; p[8]=0.1395706779261543; p[9]=0.1395706779261543;
  p[10]=0.1071592204671719; p[11]=0.1071592204671719; p[12]=0.0703660474881081;
  p[13]=0.0703660474881081; p[14]=0.0307532419961173; p[15]=0.0307532419961173;
  
  for(i=1;i&lt;=15;i++)
      {
              adapt(a, b, &amp;ptrt, &amp;ptrm, x[i]);
              if(a=0.0 &amp;&amp; b=XF) I=I+C*m*(p[i]*dfunc(t));
              else I=I+C*m*XF/2*(p[i]*dfunc(XF/2*(t+1));
  
      }
  return I;
  }
  </code></pre>
  
  <p>I wont post the main function here because it just prints and say stuff about the returns which are not important. <strong>My problem is</strong>  that it keeps giving the messages:</p>
  
  <p>"EP3.c:140:4: warning: passing argument 3 of ‘adapt’ from incompatible pointer type [enabled by default]
      adapt(a, b, &amp;ptrt, &amp;ptrm, x[i]);</p>
  
  <p>EP3.c:16:6: note: expected ‘double *’ but argument is of type ‘double **’
   void adapt(double a, double b, double *ptrt, double *ptrm, double x)"</p>
  
  <p>and the same for the other pointer. <strong>I can`t understand why does the compiler understands this pointers are "pointers to pointers"</strong></p>
  
  <p>I have looked thru the code dozens of times and cant find the reason. 
  Sorry for any mistake, first time here =)</p>