Editing Forum reference mechanisms (section)

=== Chains of references ===
Donation and leaching are not perfectly symmetric. By default, a chain of posts which all donate will recalculate the values of the posts down the chain when a new donating post is added to the chain. However, a leaching post only affects the value of the post it references – value changes from leaching do not propagate down the chain. 

For example, suppose <code>postK</code> at time <math>j</math> has value <math display="inline">R_{K,j}</math>. If <code>post1</code> with initial value <math display="inline">R_{2,0}</math> donates 0.5 to <code>post0</code>, and <code>post2</code> donates 0.7 to <code>post1</code>, then at time 2 we have <math>R_{1,2}=R_{1,1}+0.7R_{2,2}</math> and <math display="inline">R_{0,2}=R_{0,0}+0.5R_{1,1}+(0.7)(0.5)R_{2,2}</math>. So at time 2 the value from <code>post2</code> flows down through <code>post1</code> to <code>post0</code>. 

However, a post which leaches does not propagate down the chain. It only leaches value from the post it references, which does not affect any ancestors of the object post. For instance, continue the example in the previous paragraph, adding <code>post3</code> which leaches with strength -0.4. Then we get <math display="inline">R_{2,3}=(1-0.7)R_{2,2}-0.4R_{3,3} </math> and <math>R_{3,3}=R_{3,3}+0.4R_{2,2}</math> assuming the initial value of <code>post3</code> is smaller than  <math>0.4R_{2,2}</math>. The other <code>post0</code> and <code>post1</code> do not change value with the addition of <code>post3</code>. 

If the DAO wishes to leach value from several posts, it must make separate leaching references to each one.