Zhang Yuan slowly clenched his fists.
"This isn’t a do-or-die order. I know it defies the conventional wisdom on computational power."
Alchemist stood up, walked to the window, and gazed out at the pitch-black night.
"But our country needs us. No matter how Simen Zi scoffs, we have to give it our all, even if it feels like we’re just banging our heads against a wall. If we succeed, the nation will have a trump card at the negotiating table. If we fail, at least we’ll have found the limits of this approach."
Alchemist turned around and patted Zhang Yuan on the shoulder.
"Give it your all. I have to make another trip to the Capital City in the next day or two. You all just focus on building the model and running the tests without holding back. Call me if any problems come up."
Zhang Yuan saw the bloodshot veins in Alchemist’s eyes and nodded firmly.
"Understood."
Zhang Yuan picked up the documents from the desk.
"Lin Fang, let’s go. Down to the basement."
「Day One.」
The door to the lab on the second basement level slammed shut.
Zhang Yuan and Lin Fang tossed their bedrolls into a corner and turned to power on the four servers.
The room quickly filled with the roar of the fans spinning to life.
A whiteboard was pushed to the center of the room. Holding a marker, Zhang Yuan wrote out a long series of Navier-Stokes equations.
"Let’s build the sandbox model first."
Zhang Yuan stared at the whiteboard.
"Import the geometric parameters of the vehicle’s nose. We’ll start with a coarser mesh and run it once to check the boundary conditions."
Lin Fang sat at the computer, her hands a blur as they flew across the keyboard.
"Import complete. Initial mesh count: three million."
"Running the standard solver."
A green cursor blinked on the black command line.
Half an hour later, the cursor stopped.
A red prompt appeared on the screen: Equation failed to converge.
Zhang Yuan walked over and checked the error log.
"The turbulence model diverged at the tip of the nose. The mesh is too coarse; it can’t capture the details of the flow separation."
"Refine it further?" Lin Fang asked.
"Refine it."
「Day Three.」
The air in the lab was growing stale.
A few empty instant noodle containers were piled on the desk. Stubble had started to grow on Zhang Yuan’s chin.
"Increase the mesh to eight million."
Lin Fang hit the Enter key.
The server fans began to whine, sounding like a heavily loaded truck straining up a steep grade.
This time, it ran for three hours.
Zhang Yuan stood before the screen the entire time, staring at the scrolling data without blinking.
"Pressure values are rising..."
Zhang Yuan muttered to himself.
"Entering the transonic range... Mach 0.8..."
Suddenly, the scrolling data hiccuped.
Immediately after, a huge block of NaNs appeared on the screen.
The calculation had overflowed, producing invalid numbers.
"It crashed again."
Zhang Yuan slammed his fist on the desk, rattling the cup beside it.
Lin Fang rubbed her aching eyes.
"We can’t handle the nonlinear advection term. As soon as we enter the transonic range, the air’s compressibility changes abruptly, and the traditional finite difference methods just can’t maintain stability."
Zhang Yuan walked to the whiteboard, grabbed the eraser, and forcefully wiped away a section of the equations.
"We have to revise it. Let’s try an upwind scheme."
「Day Five.」
The trash can was overflowing with cigarette butts and scrap paper.
Zhang Yuan sat in his chair, staring blankly at the ceiling.
Lin Fang was asleep, slumped over the desk with a jacket draped over her shoulders.
The screen was still filled with glaring NaNs.
’They had tried every conventional approach.’
They had tried all sorts of mainstream fluid dynamics algorithms. But as soon as they increased the mesh resolution, the computational cost would explode exponentially, and the nonlinear terms would inevitably cause a collapse at some point.
If they lowered the mesh resolution, the resulting data was a garbled mess, so useless they couldn’t even use it to bluff their own side at the negotiating table.
Zhang Yuan picked up a pack of cigarettes from the desk and pulled out a crushed one. He didn’t light it, just stuck it between his lips.
A third of their twenty-day deadline was already gone.
Zhang Yuan closed his eyes, his mind filled with the arrogant smiles of the foreign representatives.
’Couldn’t figure it out in ten years, huh?’
’Were we really going to let them write us off completely?’
Zhang Yuan opened his eyes and turned to look at the soundly sleeping Lin Fang.
Zhang Yuan slowly sat up, spat out the unlit cigarette, walked over to Lin Fang, and gently shook her shoulder.
"Lin Fang, wake up."
Lin Fang groggily lifted her head, the red imprint of her sleeve still on her cheek.
"What’s wrong? Did it work?"
"No."
Zhang Yuan looked at her.
"Do you remember that matrix Chen Zhuo wrote last year?"
Lin Fang froze for a moment as her mind cleared a little.
"Chen Zhuo? Are you insane? That was for a two-dimensional model. This is a full-scale three-dimensional one. The number of mesh elements is several orders of magnitude greater."
"The logic is the same."
A fanatical gleam flickered in Zhang Yuan’s eyes—the look of a man willing to try anything in a desperate situation.
"We’re completely stuck on the continuous equations. Chen Zhuo’s approach was discrete. What if he could scale that matrix up to a higher dimension and apply it to our 3D model?"
Lin Fang looked at the data on the screen, biting her lip.
Zhang Yuan turned, walked to the desk, and snatched the receiver off the landline phone.
"Let’s get him down here. He’s our only hope."
「The Foreign Language Reading Room, Third Floor of the Old Library.」
Sunlight streamed onto a long wooden table by the window.
Chen Zhuo sat in an old wooden chair, a yellowed English monograph on the fundamental theory of algebraic topology open before him.
He read slowly, occasionally jotting down a few symbols in a nearby notebook.
Su Wei sat across from him.
In front of Su Wei sat a bulky IBM laptop, its screen filled with dense lines of financial data. She wore headphones, her brow slightly furrowed as if she were checking the historical price fluctuations of a particular stock.
It was quiet at the table, the only sounds being the rustle of turning pages and the occasional click of a mouse.
The soft sound of footsteps on the old wooden floorboards broke the silence.
The librarian from the circulation desk approached their table. He was wearing reading glasses and gently tapped twice on the edge of Chen Zhuo’s side of the table.
Chen Zhuo stopped writing and looked up.
"You’re Chen Zhuo, correct?"
The librarian lowered his voice, pointing toward the entrance.
"There’s a phone call for you at the front desk. It’s from the School of Physics. They said they called all over before tracking you down here. It sounded urgent."
Chen Zhuo paused, taken aback.
He gestured to Su Wei, then stood up and walked toward the circulation desk.
On the wooden counter sat a somewhat faded desk phone, its receiver lying beside it.
Chen Zhuo walked over and picked up the receiver.
"Hello?"
"Chen Zhuo? It’s me, Zhang Yuan."
The voice on the other end of the line was as raspy as sandpaper, and behind it, he could hear the dull roar of server fans.
Chen Zhuo shifted his stance slightly.
"Brother Zhang?"
"Didn’t interrupt your reading, did I?"
Zhang Yuan gave a bitter laugh.
"I called your dorm first. Your roommate picked up and said you’d headed to the old library with a stack of foreign-language books. I had to spend a while looking through the internal directory to find the number for this place."
Chen Zhuo listened quietly.
"What’s the matter? Is it urgent?" Chen Zhuo asked.
"It’s mission-critical."
Zhang Yuan swallowed hard on the other end of the line.
"Dean Fang managed to secure us time on the supercomputer, but we need to get the underlying algorithm working locally first. We’re completely dead in the water. The 3D transonic model won’t run, and the continuous equations keep crashing."
Through the receiver, Zhang Yuan’s voice carried a hint of undeniable helplessness.
"Chen Zhuo, I need you to come take a look."
Chen Zhuo turned his head, his gaze falling on the old camphor tree swaying in the wind outside.
"Okay. I’m on my way."
Chen Zhuo’s voice remained warm and calm.
After hanging up, Chen Zhuo walked back to his seat.
He neatly folded his scratch paper, tucked it inside the English monograph, and then put both into his backpack.
Su Wei took off one of her headphones and looked at him.
"Leaving?"
"Yeah."
Chen Zhuo packed his notebook into the backpack.
Su Wei glanced at the clock on the wall.
"It’s only two in the afternoon. Didn’t you say you were going to finish that book today?"
"Something came up at the School of Physics."
Chen Zhuo zipped up his backpack.
"My senior from the lab called me. It sounds like they’re in a tough spot."
Chen Zhuo looked back at Su Wei, the corners of his mouth lifting into a slight smile.
"I’m going to see if I can help. The book can wait."
Su Wei said nothing more, simply put her headphones back on, her eyes returning to the financial data on her screen.
"See you tomorrow."
"See you tomorrow."

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