Ok, this is leaving me increasingly frustrated. This builds on a previous question here but I am still not getting the indexing, although I learned from that question all the same.
Case 1: First convolution equation example:
h[k]∗h∗[−k]=∞∑n=−∞h[n] h∗[n+k]
The way I got the right hand side, was:
1) Make the h's have dummy variables, so h[n] and h∗[−n].
2) Flip one of them around, so now I get h[n] and h∗[n]
3) Add the delay k into the one that way flipped, so finally I have ∑∞n=−∞h[n] h∗[n+k].
Great, I have a convolution.
Case 2: Second convolution example: (Unrelated to first)
We have:
∞∑i=−∞h[i−m] Rxx[i].
Here we want to try and find out what convolution this corresponds to. The way to solve this, (apparently), is to make the assumption that another variable g[n]=h[−n], and call it a day. Then we get:
∞∑i=−∞h[i−m] Rxx[i]=∞∑i=−∞g[−(i−m)] Rxx[i]=∞∑i=−∞g[m−i] Rxx[i]=g[m]∗Rxx[m]=h[−m]∗Rxx[m]
This works great.
Case3: The problem:
This is my problem. Case 1 showed the steps for how to do a normal convolution. Case 2 showed how the method of substitution works. However, if I try to solve Case 1 using this substitution method, I get the wrong answer, even though it worked on case 2. Why is that?
To wit - where am I going wrong here?
h[k]∗h∗[−k]=h[k]∗g∗[k]=∞∑n=−∞h[n] g∗[k−n]=∞∑n=−∞h[n] h∗[−(k−n)]=∞∑n=−∞h[n] h∗[n−k]
However, this is **clearly* the wrong answer! What am I doing wrong here?
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