how to use correlation function main definition?












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I'm enrolled in a course off control where the formula for correlation was presented to us without any context .



$RX(t1,t2) = intint x1x2 fX(t1)X(t2)(x1,x2)dx1dx2$



the problema than I'm facing is then when we calculate for instances the correlation of X(t)=Acos(wt+a) ,where a is a uniform random variable in the interval [0,2$pi$] we do the following :



$RX(t1,t2) = frac{1}{2pi}int_{0}^{2pi}cos(wt1 + a)cos(wt2+a)da$



what happened to the double integral,and why is there only the integral in a and not two in a1 and a2 ? I apologize for the trivial question but has it is probably to obvious for someone who knows the meaning of the elements of the formula I couldn't find an explanation in the internet.










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    $begingroup$


    I'm enrolled in a course off control where the formula for correlation was presented to us without any context .



    $RX(t1,t2) = intint x1x2 fX(t1)X(t2)(x1,x2)dx1dx2$



    the problema than I'm facing is then when we calculate for instances the correlation of X(t)=Acos(wt+a) ,where a is a uniform random variable in the interval [0,2$pi$] we do the following :



    $RX(t1,t2) = frac{1}{2pi}int_{0}^{2pi}cos(wt1 + a)cos(wt2+a)da$



    what happened to the double integral,and why is there only the integral in a and not two in a1 and a2 ? I apologize for the trivial question but has it is probably to obvious for someone who knows the meaning of the elements of the formula I couldn't find an explanation in the internet.










    share|cite|improve this question











    $endgroup$















      0












      0








      0





      $begingroup$


      I'm enrolled in a course off control where the formula for correlation was presented to us without any context .



      $RX(t1,t2) = intint x1x2 fX(t1)X(t2)(x1,x2)dx1dx2$



      the problema than I'm facing is then when we calculate for instances the correlation of X(t)=Acos(wt+a) ,where a is a uniform random variable in the interval [0,2$pi$] we do the following :



      $RX(t1,t2) = frac{1}{2pi}int_{0}^{2pi}cos(wt1 + a)cos(wt2+a)da$



      what happened to the double integral,and why is there only the integral in a and not two in a1 and a2 ? I apologize for the trivial question but has it is probably to obvious for someone who knows the meaning of the elements of the formula I couldn't find an explanation in the internet.










      share|cite|improve this question











      $endgroup$




      I'm enrolled in a course off control where the formula for correlation was presented to us without any context .



      $RX(t1,t2) = intint x1x2 fX(t1)X(t2)(x1,x2)dx1dx2$



      the problema than I'm facing is then when we calculate for instances the correlation of X(t)=Acos(wt+a) ,where a is a uniform random variable in the interval [0,2$pi$] we do the following :



      $RX(t1,t2) = frac{1}{2pi}int_{0}^{2pi}cos(wt1 + a)cos(wt2+a)da$



      what happened to the double integral,and why is there only the integral in a and not two in a1 and a2 ? I apologize for the trivial question but has it is probably to obvious for someone who knows the meaning of the elements of the formula I couldn't find an explanation in the internet.







      correlation






      share|cite|improve this question















      share|cite|improve this question













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      share|cite|improve this question








      edited Jan 14 at 11:57







      ricostynha

















      asked Jan 14 at 10:55









      ricostynharicostynha

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