I have created a Matlab Simulink model with a series of dot products.


Embedded Coder generates a for loop for each dot product, as evidenced by this excerpt of the generated output:

/* DotProduct: '<S3>/Dot Product1' incorporates:
 *  Inport: '<Root>/LngPwr'
EPAR_SPAF_dot_B.DotProduct1 = 0.0F;
for (temp_ = 0; temp_ < 24; temp_++) {
  EPAR_SPAF_dot_B.DotProduct1 += temp_DataTypeConversion[temp_] *
/* End of DotProduct: '<S3>/Dot Product1' */

/* DotProduct: '<S3>/Dot Product2' incorporates:
 *  Inport: '<Root>/ShrtPwr'
EPAR_SPAF_dot_B.DotProduct2 = 0.0F;
for (temp_ = 0; temp_ < 24; temp_++) {
  EPAR_SPAF_dot_B.DotProduct2 += temp_DataTypeConversion[temp_] *
/* End of DotProduct: '<S3>/Dot Product2' */

Can I improve the Simulink model such that it will compile to better code?

I want to avoid using embedded matlab or a S-function for the purposes of maintainability.

  • 4
    \$\begingroup\$ I find this kind of downvoting to be extremely frustrating because it communicates to me that there is a total lack of understanding of how MATLAB Simulink and Embedded Coder works. There IS Working code in the original post, it just happens to be graphical. The C-Code is auto generated. The question is identical to any kind of other Code efficiency question since the way you craft the simulink will directly affects the C-Code generated which in turns affects how it runs on the target. \$\endgroup\$ – Michael Coury May 6 '16 at 12:49
  • \$\begingroup\$ @MichaelCoury Stackoverflow has the tag matlab, why don't you try it there? There's also scicomp.stackexchange.com \$\endgroup\$ – Niklas R. May 6 '16 at 14:49
  • \$\begingroup\$ @Programmer400, Thanks for the constructive feedback, I'll see what the Stackoverflow community looks like. Having said that, CodeReview also has a matlab tag, so... I still pretty confident that this question falls into the realm of CodeReview IF the scope of CodeReview includes optimization. I am going to continue this conversation in the meta section.... \$\endgroup\$ – Michael Coury May 6 '16 at 15:24
  • 2
    \$\begingroup\$ This question is being discussed on Meta. \$\endgroup\$ – 200_success May 6 '16 at 16:21

There is a common mathematical operation involving many dot products: it's called matrix multiplication.

$$ \left[\begin{matrix}v_1 & v_2 & v_3 & v_4\end{matrix}\right] \left[\begin{matrix} a_1 & b_1 & c_1 \\ a_2 & b_2 & c_2 \\ a_3 & b_3 & c_3 \\ a_4 & b_4 & c_4 \end{matrix}\right] = \left[\begin{matrix}(\vec{v}\cdot\vec{a}) & (\vec{v}\cdot\vec{b}) & (\vec{v}\cdot\vec{c})\end{matrix}\right] $$

So, I recommend that you concatenate vectors \$\color{lightgreen}1\$ to \$\color{lightgreen}6\$ into a matrix and perform matrix multiplication.

Illustrated matrix multiplication

You can also transpose and swap the matrices:

$$ \left[\begin{matrix} a_1 & a_2 & a_3 & a_4 \\ b_1 & b_2 & b_3 & b_4 \\ c_1 & c_2 & c_3 & c_4 \\ \end{matrix}\right] \left[\begin{matrix}v_1 \\ v_2 \\ v_3 \\ v_4\end{matrix}\right] = \left[\begin{matrix}\vec{a}\cdot\vec{v} \\ \vec{b}\cdot\vec{v} \\ \vec{c}\cdot\vec{v}\end{matrix}\right] $$

| improve this answer | |
  • \$\begingroup\$ Gosh, I wish I was better at linear algebra... I'll put this into Simulink and Embedded Coder and see what the output looks like... \$\endgroup\$ – Michael Coury May 6 '16 at 23:54

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