mjbWorld

On the page titled "<a href="http://www.euclideanspace.com/maths/algebra/matrix/functions/determinant/fourD/index.htm">Maths - Matrix algebra - Determinants 4D</a>", there is a typo:

<span style="margin-left: 1em">The following calculator allows you to calculate the determinant for a <u>3x3</u> matrix.</span>

The matrix on this page is a <u>4x4</u>, not 3x3.

Also, immediately above it, after the text:

<span style="margin-left: 1em">The Laplace Expansion gives:</span>

has a table with m00* (table 1) -m01* (table 2) +m02* (table 3) -m03* (table 4), where the "<b>m0_</b>" is left-aligned:

<table width="100%" border="0"> <tr> <td>m00*</td> <td><table width="100%" border="1"> <tr> <td>m11</td> <td>m12</td> <td>m13</td> </tr> <tr> <td>m21</td> <td>m22</td> <td>m23</td> </tr> <tr> <td>m31</td> <td>m32</td> <td>m33</td> </tr>

</table></td>
<td>-m01*</td>
<td><table width="100%" border="1">
  <tr>
    <td>m10</td>
    <td>m12</td>
    <td>m13</td>
  </tr>
  <tr>
    <td>m20</td>
    <td>m22</td>
    <td>m23</td>
  </tr>
  <tr>
    <td>m30</td>
    <td>m32</td>
    <td>m33</td>
  </tr>

</table></td>
<td>+m02*</td>
<td><table width="100%" border="1">
  <tr>
    <td>m10</td>
    <td>m11</td>
    <td>m13</td>
  </tr>
  <tr>
    <td>m20</td>
    <td>m21</td>
    <td>m23</td>
  </tr>
  <tr>
    <td>m30</td>
    <td>m31</td>
    <td>m33</td>
  </tr>

</table></td>
<td>-m03*</td>
<td><table width="100%" border="1">
  <tr>
    <td>m10</td>
    <td>m11</td>
    <td>m12</td>
  </tr>
  <tr>
    <td>m20</td>
    <td>m21</td>
    <td>m22</td>
  </tr>
  <tr>
    <td>m30</td>
    <td>m31</td>
    <td>m32</td>
  </tr>

</table></td>

</tr> </table>

It would probably make it more readable by right-aligning the "<b>m0_</b>" instead of left-aligned.

This is what I propose:

<table width="100%" border="0"> <tr> <td align="right"><b>m00*</b></td> <td><table width="100%" border="1"> <tr> <td>m11</td> <td>m12</td> <td>m13</td> </tr> <tr> <td>m21</td> <td>m22</td> <td>m23</td> </tr> <tr> <td>m31</td> <td>m32</td> <td>m33</td> </tr>

</table></td>
<td align="right"><b>-m01*</b></td>
<td><table width="100%" border="1">
  <tr>
    <td>m10</td>
    <td>m12</td>
    <td>m13</td>
  </tr>
  <tr>
    <td>m20</td>
    <td>m22</td>
    <td>m23</td>
  </tr>
  <tr>
    <td>m30</td>
    <td>m32</td>
    <td>m33</td>
  </tr>

</table></td>
<td align="right"><b>+m02*</b></td>
<td><table width="100%" border="1">
  <tr>
    <td>m10</td>
    <td>m11</td>
    <td>m13</td>
  </tr>
  <tr>
    <td>m20</td>
    <td>m21</td>
    <td>m23</td>
  </tr>
  <tr>
    <td>m30</td>
    <td>m31</td>
    <td>m33</td>
  </tr>

</table></td>
<td align="right"><b>-m03*</b></td>
<td><table width="100%" border="1">
  <tr>
    <td>m10</td>
    <td>m11</td>
    <td>m12</td>
  </tr>
  <tr>
    <td>m20</td>
    <td>m21</td>
    <td>m22</td>
  </tr>
  <tr>
    <td>m30</td>
    <td>m31</td>
    <td>m32</td>
  </tr>

</table></td>

</tr> </table>

Wow; the "instant preview" showed that correctly. I guess it got unescaped.

Okay, for the first part, the text says that there's a 3x3 matrix (on the website linked in the original post), but the matrix is actually 4x4.

Second, I recommended right-aligning all of the "m00 ***", "-m01 *", "+m02 ***" and "**-m03 ***" instead of the default left-align for easier readability.

Let's see if THIS is easier to read. I had not found an "edit post" else I would have just corrected the original :-/

Thank you very much, I have made the changes that you suggested. I also removed the: width="100%" from the table (this means that the right justification has less effect) but I think its best to do this as display screens are getting wider and so the table might get more stretched.

Cheers,

Martin

Another typo, another page. Do you want these in a single thread, or put in separate ones? I'd rather not create tons of threads if I find one here, and another there... Unless that's better for the devs, who may not follow deep threads.

On http://www.euclideanspace.com/threed/scenegraph/index.htm, the word "on" near the end should be "one":

"Java3d does not allow most nodes to be parented by more than on node"

Same page, above that one:

"the branches grow back together., XML supports a tree only."

There's a period followed by a comma.

Further down:

"Acyclic means that there cant be loops, i.e. child cant be one of its own ancestors"

"cant" needs to be "can't" in two places, and there is no period at the end of the sentence.

...further down, 2nd paragraph from bottom:

"you always end up at a leaf eventually:"

This is the last sentence, before a <hr> and the start of the "Nodes" section.

Last sentence:

" modifies all of the shapes below it by transforming their veracities through a 4x4 matrix."

"veracities" may be correct here, but kinda sounds hokey. Its meaning is "truth", but how does that fit in the context of this paragraph? Could another word be used in its place for clarification?

sigh Again, a post because I don't see an "edit" button...

When I was commenting on the "This is the last sentence, before a <hr> and the start of the "Nodes" section.", I meant to also say that it ends with a colon, which should probably be a period.

teamterradactyl,

Thanks very much I have made these corrections to the webpage.

I think "veracities" must have happened when I was using the spelling checker, I must have allowed a substitution in error, I intended to say vertices!

I appreciate the corrections, so please feel free to use whatever form is easiest, a single thread would be fine.

I assume the lack of an "Edit" function on the forum is a limitation of the Sourceforge software? I haven't seen any parameters that would allow me, as admin, to enable any features like that.

Martin

Another page where a sentence (or two) can use a little revision:

http://www.euclideanspace.com/physics/mechanics/statics/forces/index.htm

"We also need to know if objects are in equilibrium or are they going to start accelerating in some direction To do this we need to model forces, is there any way that this can be done by the program itself from its database of the properties of objects in its world, without being explicitly told about where the forces are acting?"

I might suggest:

"We also need to know whether objects are in equilibrium, or whether they are going to start accelerating in some direction. To do this, we need to model forces. Is there any way that this can be done by the program itself from its database of the properties of objects in its world, without being explicitly told about where the forces are acting?"

==========

Lower on the same page:

"If the system of forces are in ballence then the point we choose to measure the couple around is just a matter of choosing the most convienent point for the calculations because if its in ballance around one point its in ballance around all points. However, if the forces are not in ballance, it is important and we will want to find the axis where the couple can be consided to act."

I might suggest:

"If the system of forces are in balance, then the point that we choose to measure the couple around is just a matter of choosing the most convenient point for the calculations. This is because, if it is in balance around one point, it is in balance around all points. However, if the forces are not in balance, it is important and we will want to find the axis where the couple can be consided to act."

==========

Under the "Twists" section, there is no information.

==========

Under the "Wrenches" section:

"A Wrench is the resultant of both the linear and rotational forces, this can be made up of two vectors"

...to...

"A Wrench is the resultant of both the linear and rotational forces. This can be made up of two vectors."

(add two periods: after "forces" and after "vectors")

==========

Under the "Other Forces" section:

"Other forces may be modeled, such as springs, electromagnetic, etc. these are covered in further sections."

(capitalize "these")

==========

Later:

"...the magnitude of the force only needs to be stores once."

On page http://www.euclideanspace.com/threed/games/examples/snooker/rolling/index.htm

"So the angular velocity is directly linked to linear velocity, so can we work directly from the linear velocity in our program? calculating angular velocity from linear velocity when required.

Of course, this assumes that assumes that there is no slipping, for that to be true the linear momentum must be exactly matched to the rotational momentum."

...to...

"So the angular velocity is directly linked to linear velocity. Can we work directly from the linear velocity in our program, calculating angular velocity from linear velocity when required?

Of course, this assumes that there is no slipping. For that to be true the linear momentum must be exactly matched to the rotational momentum."

Thanks OnlineCop,

I have corrected these pages as you suggest.

I realise that my grammar and spelling are bad, but I do think they are very important, so I appreciate these corrections.

Martin