The hallway in the School of Physics’ underground laboratory was long, and the incandescent lights overhead emitted a faint electrical hum.
Chen Zhuo came down the stairs and pushed open the soundproof door at the end of the hall.
A thick smell of smoke hit him, mixed with the hot air blowing from the vents of the computer cases.
Zhang Yuan was sitting in front of the center computer, his hands raking through his already messy hair. His eyes were heavily bloodshot, and his lips were dry and chapped.
Lin Fang sat at a desk on the other side, a thick stack of printouts in her hands. She was going over the data line by line with a red pen. She raised a hand to rub her brow, then picked up the enamel mug on her desk and took a sip. Her brow furrowed slightly. The water was clearly ice-cold.
Hearing the door open, they both turned around.
"Seniors."
Chen Zhuo closed the door behind him and set his backpack on a nearby empty desk.
Zhang Yuan shot up as if he’d been thrown a lifeline, pushing his swivel chair back to clear a space.
"You’re finally here. Sit."
Zhang Yuan pointed at the screen.
Chen Zhuo walked over, but he didn’t sit down right away. He glanced at the screen first.
It was a 3D model of the front of a train, composed of a countless, dense mesh of grid lines.
The lines were packed so densely they blurred into a patch of glaring green. A few black command-line windows ran alongside it, but the cursor was frozen, unable to produce a new data point for what felt like an eternity.
"Frozen solid?" Chen Zhuo asked.
"It’s been frozen for three hours."
Zhang Yuan fumbled on the desk for his pack of cigarettes, pulled one out, and stuck it between his lips. After patting his pockets for a long time and finding no lighter, he gave up, taking the cigarette out of his mouth and tossing it aside.
"The memory’s maxed out, and CPU usage has been at one hundred percent. If this junker keeps churning like this, I’m afraid the motherboard is going to fry."
Chen Zhuo pulled a chair over and sat. He placed his hand on the mouse and moved the cursor slightly. The screen stuttered badly; there was a significant lag when he tried to drag the model.
"New requirements from the Ministry of Railways?" Chen Zhuo asked, his eyes still on the screen.
Lin Fang put down her paper cup and nodded.
"The second round of talks is at the beginning of next month. The teams from Siemens and Kawasaki are already in the Capital City."
"They won’t give us the aerodynamic data?"
"They’re not leaking a thing."
Zhang Yuan scoffed and slammed his palm on the desk.
"Not only are they withholding the data, they’re cornering us on the price. They know damn well our domestic high-speed wind tunnels can’t generate full-scale, trans-sonic data at this stage."
Lin Fang leaned back in her chair, her gaze drifting up to the incandescent lights on the ceiling.
"Their representative was nasty at the meeting. He implied that because our domestic tunnel cross-sections are different from theirs, people would die if we just slap our own train front on without their proprietary aerodynamic data. As for the micro-pressure wave problem... he said we wouldn’t be able to figure it out on our own in a decade."
Chen Zhuo remained silent, his gaze fixed on the long, complex string of partial differential equations on the right side of the screen.
The traditional Navier-Stokes equations.
In three-dimensional space, the sheer number of boundary conditions was enough to make your scalp crawl.
"This approach is a dead end."
Zhang Yuan gestured toward the equations.
"With continuous fluid dynamics equations in a three-dimensional trans-sonic state, the non-linear terms just explode. The machines we have in this lab can’t even compute a single initial boundary condition."
Chen Zhuo took his hand off the mouse and turned to face Zhang Yuan.
"What do you want me to do?"
Zhang Yuan swallowed hard, a flicker of hope in his eyes.
"Didn’t you help us with a dimensionality reduction algorithm last year?"
Zhang Yuan made a gesture with his hands.
"That Discrete Matrix. You cut out the infinity from the time slices and calculated the abrupt pressure change over 0.01 seconds."
Lin Fang also sat up straighter.
"Chen Zhuo, we’ve discussed this. Since we can’t compute the continuous equations, we were wondering if we could use the same trick again. Can we apply your Discrete Matrix method to this three-dimensional model?"
"Break the entire three-dimensional train front into discrete grid points," Zhang Yuan added.
"We’ll stop trying to solve the continuous equations and just compute the matrix instead. Your algorithm’s error control is excellent. As long as we can make the mesh fine enough, we’ll have a trump card with enough precision to shove right back in their faces at the negotiating table."
Chen Zhuo listened quietly until they had finished.
He looked at Zhang Yuan and Lin Fang’s bloodshot eyes.
He knew perfectly well the mathematical and logical hurdles they would face by forcibly extending a two-dimensional planar Discrete Matrix to a full-scale three-dimensional model.
"Do you still have the source code for my Discrete Matrix’s underlying logic?" Chen Zhuo asked.
"Yes! It’s all in the repository."
Zhang Yuan quickly tapped a few keys, pulling up a document filled with code.
Chen Zhuo leaned closer to the screen and studied it for a moment.
"To apply this to the 3D model, we’ll have to expand the matrix dimensions. The original Jacobian matrix won’t work anymore. We’ll need to add non-linear compensation."
Chen Zhuo’s tone was perfectly level.
"Can you change it?" Zhang Yuan asked.
"Get me a pen and paper."
Zhang Yuan immediately spun around, pulled a stack of A4 paper from the tray of a nearby printer, and handed it to Chen Zhuo along with a pen.
Chen Zhuo set the paper on the desk and uncapped the pen.
He wrote deliberately, not quickly. Each line of the expanded matrix required him to account for coordinate system transformations in three-dimensional space.
Zhang Yuan and Lin Fang stood behind him, hardly daring to breathe.
After filling two pages, Chen Zhuo stopped writing and pushed the second page in front of Zhang Yuan.
"I’ve scaled up the dimensions."
Chen Zhuo pointed to a set of formulas on the page.
"I also changed the logic for the mesh partitioning. Replace the old code in the core program with these segments and rebuild the mesh."
Zhang Yuan snatched up the paper, moved to the computer next to Chen Zhuo, and his hands began to fly across the keyboard.

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